Remove deps
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
85b88be2a4