Remove unnecessary _PyCapsule class definition and import for clarity

Author: kosiew

python/datafusion/user_defined.py

@@ -41,13 +41,8 @@
 from datafusion.expr import Expr
 
 if TYPE_CHECKING:
-    from _typeshed import CapsuleType as _PyCapsule
-
     _R = TypeVar("_R", bound=pa.DataType)
-else:
 
-    class _PyCapsule:
-        """Lightweight typing proxy for CPython ``PyCapsule`` objects."""
 
 
 class Volatility(Enum):