Remove exception-handler lexing from unused-bound-exception fix (#5851)

## Summary

The motivation here is that it will make this rule easier to rewrite as
a deferred check. Right now, we can't run this rule in the deferred
phase, because it depends on the `except_handler` to power its autofix.
Instead of lexing the `except_handler`, we can use the `SimpleTokenizer`
from the formatter, and just lex forwards and backwards.

For context, this rule detects the unused `e` in:

```python
try:
  pass
except ValueError as e:
  pass
```

crates/ruff_python_formatter/Cargo.toml

@@ -28,7 +28,6 @@ rustpython-parser = { workspace = true }
 serde = { workspace = true, optional = true }
 smallvec = { workspace = true }
 thiserror = { workspace = true }
-unic-ucd-ident = "0.9.0"
 
 [dev-dependencies]
 ruff_formatter = { path = "../ruff_formatter", features = ["serde"]}