After this pull request merged:
https://github.com/servo/servo/pull/7209
the 'script' component would never enter a 'built' state. In other
words, if one calls `mach build`, lets it complete, then calls `mach
build` again, the 'script' component would rebuild even though we
supposedly just built it. This was due to the `ParserResults.pkl`
getting placed in the `components/script` directory instead of the
output directory, causing cargo to think that there were unbuilt files.
Prior to this commit, the script codegen makefile relied on an
intermediary pythonpath.py file that handled python dependencies and
incorporated a couple hacks to get the codegen building working. This
commit removes that intermediary file and attempts to make the script
codegen build process cleaner.
This is necessary to ensure Cargo knows when to rebuild. Normally
.gitignore would be enough to exclude these from Cargo's freshness
calculation, but https://github.com/rust-lang/cargo/issues/1729 prevents
this currently. This is the new, correct way to do these thigns, just
like the style crate does.
