Remove cruft from generate build script

[torben-hansen]

Description of changes:

Removes 50% of the code from generate_build_files.py which are never used. Probably a remnant from years ago when first changing this script to feed AWS-LC needs.

Consuming Perl-generated machine implementations and Go generated files are done by cmake scripts.

Testing:

First check script generates the same folder

$ cp -r generated-src/ ../generated_source
$ rm -rf ./generated-src
$ python3 util/generate_build_files.py 
$ diff -rq generated-src/ ../generated_source/
<empty>
$ git diff
<empty>

Check build without Perl

$ cmake3 -GNinja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$(pwd)/../awslc-install -DBUILD_SHARED_LIBS=OFF -DDISABLE_PERL=ON .. 
$ ninja-build run_tests

[...]

All tests passed!

Check build without Go

$ cmake3 -GNinja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$(pwd)/../awslc-install -DBUILD_SHARED_LIBS=OFF -DDISABLE_GO=ON .. 
$ ninja-build
$ ./crypto/crypto_test

[...]

[  PASSED  ] 1421 tests.

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the ISC license.