Remove redundant import pyarrow as pa from docstrings

The pa alias is already provided by the doctest namespace in
conftest.py, so inline imports are unnecessary.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

python/datafusion/user_defined.py

@@ -213,7 +213,6 @@ def udf(*args: Any, **kwargs: Any):  # noqa: D417
         Examples:
             Using ``udf`` as a function:
 
-            >>> import pyarrow as pa
             >>> import pyarrow.compute as pc
             >>> from datafusion.user_defined import ScalarUDF
             >>> def double_func(x):
@@ -480,7 +479,6 @@ def udaf(*args: Any, **kwargs: Any):  # noqa: D417, C901
         instance in which this UDAF is used.
 
         Examples:
-            >>> import pyarrow as pa
             >>> import pyarrow.compute as pc
             >>> from datafusion.user_defined import AggregateUDF, Accumulator, udaf
             >>> class Summarize(Accumulator):
@@ -874,7 +872,6 @@ def udwf(*args: Any, **kwargs: Any):  # noqa: D417
               When using ``udwf`` as a decorator, do not pass ``func`` explicitly.
 
         Examples:
-            >>> import pyarrow as pa
             >>> from datafusion.user_defined import WindowUDF, WindowEvaluator, udwf
             >>> class BiasedNumbers(WindowEvaluator):
             ...     def __init__(self, start: int = 0):