Revert "Improve interface."

This reverts commit 94b39a5.

src/antsibull/versions.py

@@ -119,14 +119,14 @@ def feature_freeze_version(spec: str, collection_name: str) -> str:
     return _FeatureFreezeVersion(spec, collection_name).compute_new_spec()
 
 
-def load_constraints_if_exists(filename: str | os.PathLike[str]) -> dict[str, SemVerSpec]:
+def load_constraints_if_exists(filename: str) -> dict[str, SemVerSpec]:
     """
     Load a constraints file, if it exists.
     """
     result: dict[str, SemVerSpec] = {}
     if not os.path.exists(filename):
         return result
-    for line in parse_pieces_file(os.fspath(filename)):
+    for line in parse_pieces_file(filename):
         record = [entry.strip() for entry in line.split(":", 1)]
         if len(record) < 2:
             raise ValueError(