tidy: Remove cargo check.

The cargo check was checking that every dependency had an `extern crate`.
The compiler has not used `extern crate` in a long time (edition 2018).
The test was broken (the call to `!super::filter_dirs(path)` was backwards).
This just removes it since it is no longer valid.

src/tools/tidy/src/lib.rs

@@ -40,7 +40,6 @@ macro_rules! tidy_error {
 }
 
 pub mod bins;
-pub mod cargo;
 pub mod debug_artifacts;
 pub mod deps;
 pub mod edition;

src/tools/tidy/src/main.rs

@@ -49,10 +49,6 @@ fn main() {
     style::check(&compiler_path, &mut bad);
     style::check(&library_path, &mut bad);
 
-    cargo::check(&src_path, &mut bad);
-    cargo::check(&compiler_path, &mut bad);
-    cargo::check(&library_path, &mut bad);
-
     edition::check(&src_path, &mut bad);
     edition::check(&compiler_path, &mut bad);
     edition::check(&library_path, &mut bad);