Remove HashMap and HashSet for known-standard-library detection (#5345)

## Summary

This is a lot more concise and probably much more performant (with fewer
instructions).

crates/ruff_python_stdlib/Cargo.toml

@@ -13,5 +13,3 @@ license = { workspace = true }
 [lib]
 
 [dependencies]
-once_cell = { workspace = true }
-rustc-hash = { workspace = true }