Remove needless sort in _style_guide_for

We are always returning the last element so a 'max' operation is sufficient instead of sorting. Note the old code did not handle an empty list so this change doesn't either

Author: mxr

src/flake8/style_guide.py

@@ -254,13 +254,10 @@ def populate_style_guides_with(
 
     def _style_guide_for(self, filename: str) -> "StyleGuide":
         """Find the StyleGuide for the filename in particular."""
-        guides = sorted(
+        return max(
             (g for g in self.style_guides if g.applies_to(filename)),
             key=lambda g: len(g.filename or ""),
         )
-        if len(guides) > 1:
-            return guides[-1]
-        return guides[0]
 
     @contextlib.contextmanager
     def processing_file(