Remove deps

[Jarcho]

This remove both regex and cargo_metadata as dependencies making clippy_dev compile ~3x faster (~46s -> ~16s locally). cargo_metadata was used to extract the version field from Cargo.toml, which is done trivially without that. regex was used to parse define_clippy_lint in update_lints which is now done using rustc_lexer. This isn't any simpler, but it compiles ~15s faster and runs ~3x faster (~2.1s -> ~0.7s locally).

The next biggest offenders to compile times are clap and winapi on windows. clap could be removed, but re-implementing enough is probably more work than it's worth. winapi is used by opener and walkdir so it's stuck there.

changelog: none

[rust-highfive]

r? @camsteffen

(rust-highfive has picked a reviewer for you, use r? to override)

[xFrednet]

This looks interesting. I'll take over the review to take some load of off @camsteffen. I'll review this over the week :)

r? @xFrednet

[xFrednet]

This is a solid improvement and excellent work. I have one comment and some nits, but just little things.

The changes also had a major improvement for my compilation performance, it cut 30 seconds down to ~9 seconds. And the code is also more readable, IMO. Okay, enough praise 🙃

[xFrednet]

Everything looks good to me, thank you for this change. I think everyone is going to enjoy the faster compile time for clippy_dev 🎉

@bors r+

[bors]

📌 Commit ae5af0c has been approved by xFrednet

[bors]

⌛ Testing commit ae5af0c with merge 85b88be...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing 85b88be to master...