tidy: Replace custom panic/unwrap lint with clippy lint (#38593)

This change replaces our custom `panic` / `unwrap` lint with the one
from clippy. This rule as not properly applied in servoshell, so this
change fixes some clippy errors raised by the new configuration.

Testing: This change removes the tidy tests for the custom lints, but
otherwise the behavior is tested as part of clippy itself.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

python/tidy/tests/rust_tidy.rs

@@ -78,8 +78,4 @@ impl test {
     } else {
         let xif = 42 in {  xif  } // Should not trigger
     }
-
-    let option = Some(3);
-    println!("{}", option.unwrap());
-    panic!("What a way to end.");
 }