Fix various warnings

[fgsch]

Fix various warnings spotted by clippy.

[fgsch]

And the list of warnings this PR is trying to silence:

    Checking viceroy-lib v0.5.2 (/Users/fgsch/foss/Viceroy/lib)
warning: the borrowed expression implements the required traits
   --> lib/src/config/geolocation.rs:211:39
    |
211 |         let data = fs::read_to_string(&file).map_err(GeolocationConfigError::IoError)?;
    |                                       ^^^^^ help: change this to: `file`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `#[warn(clippy::needless_borrow)]` on by default

warning: the borrowed expression implements the required traits
  --> lib/src/config/secret_store.rs:81:34
   |
81 |                         fs::read(&path)
   |                                  ^^^^^ help: change this to: `path`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

warning: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
   --> lib/src/session.rs:893:23
    |
893 |         let targets = std::mem::replace(&mut self.targets, Vec::new());
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::mem::take(&mut self.targets)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_default
    = note: `#[warn(clippy::mem_replace_with_default)]` on by default

warning: casting to the same type is unnecessary (`u64` -> `u64`)
   --> lib/src/execute.rs:356:37
    |
356 |             bytesize::ByteSize::kib(heap_pages as u64 * 64)
    |                                     ^^^^^^^^^^^^^^^^^ help: try: `heap_pages`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
    = note: `#[warn(clippy::unnecessary_cast)]` on by default

warning: useless conversion to the same type: `body::Chunk`
  --> lib/src/streaming_body.rs:59:19
   |
59 |             .send(Chunk::from(chunk.into()).into())
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `Chunk::from()`: `chunk.into()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion
   = note: `#[warn(clippy::useless_conversion)]` on by default

warning: redundant clone
  --> lib/src/streaming_body.rs:81:41
   |
81 |                 let sender = self.sender.clone();
   |                                         ^^^^^^^^ help: remove this
   |
note: this value is dropped without further use
  --> lib/src/streaming_body.rs:81:30
   |
81 |                 let sender = self.sender.clone();
   |                              ^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
   = note: `#[warn(clippy::redundant_clone)]` on by default

warning: useless conversion to the same type: `wiggle_abi::types::PendingRequestHandle`
   --> lib/src/wiggle_abi/req_impl.rs:599:44
    |
599 |         let handle: PendingRequestHandle = pending_req_handle.into();
    |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `pending_req_handle`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion

warning: this expression creates a reference which is immediately dereferenced by the compiler
   --> lib/src/wiggle_abi/secret_store_impl.rs:113:39
    |
113 |         plaintext_out.copy_from_slice(&plaintext);
    |                                       ^^^^^^^^^^ help: change this to: `plaintext`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

warning: `viceroy-lib` (lib) generated 8 warnings (run `cargo clippy --fix --lib -p viceroy-lib` to apply 8 suggestions)
    Checking viceroy v0.5.2 (/Users/fgsch/foss/Viceroy/cli)
warning: the borrowed expression implements the required traits
   --> cli/src/opts.rs:197:34
    |
197 |     let contents = std::fs::read(&path)?;
    |                                  ^^^^^ help: change this to: `path`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `#[warn(clippy::needless_borrow)]` on by default

warning: this expression creates a reference which is immediately dereferenced by the compiler
  --> cli/src/main.rs:42:40
   |
42 |     let ctx = create_execution_context(&serve_args.shared(), true).await?;
   |                                        ^^^^^^^^^^^^^^^^^^^^ help: change this to: `serve_args.shared()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

warning: this expression creates a reference which is immediately dereferenced by the compiler
  --> cli/src/main.rs:88:40
   |
88 |     let ctx = create_execution_context(&run_args.shared(), false).await?;
   |                                        ^^^^^^^^^^^^^^^^^^ help: change this to: `run_args.shared()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

[aturon]

These all LGTM, thank you!