Remove virtual memory support

[Robbepop]

Benchmarks show that the virtual_memory support in wasmi actually regresses performance compared to the naive Vec-based implementation. Also it complicates configuration space and therefore makes testing more difficult.
Furthermore we do not have a real use for virtual memory in Substrate or Polkadot for wasmi.

This feature also prevented us from using windows-latest in CI and we had to fall back onto windows-2019.

[codecov-commenter]

Codecov Report

Merging #408 (a58ece9) into master (baab359) will increase coverage by 0.50%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #408      +/-   ##
==========================================
+ Coverage   76.22%   76.73%   +0.50%     
==========================================
  Files          70       68       -2     
  Lines        6788     6743      -45     
==========================================
  Hits         5174     5174              
+ Misses       1614     1569      -45     

Impacted Files	Coverage Δ
wasmi_v1/src/memory/byte_buffer.rs	89.47% <ø> (ø)
wasmi_v1/src/memory/mod.rs	68.69% <0.00%> (+1.74%)	⬆️

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