docs: drop trailing clear_sender_ctx from set_sender_ctx example

The trailing cleanup call was test hygiene, not API teaching, and
risked implying callers must always pair set with clear. Adjacent
clear_sender_ctx and get_sender_ctx doctests are self-contained
(they explicitly set or clear before asserting), so removing the
cleanup line does not affect doctest outcomes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

python/datafusion/ipc.py

@@ -175,14 +175,11 @@ def set_sender_ctx(ctx: SessionContext) -> None:
 
     Examples:
         >>> from datafusion import SessionContext
-        >>> from datafusion.ipc import (
-        ...     set_sender_ctx, get_sender_ctx, clear_sender_ctx,
-        ... )
+        >>> from datafusion.ipc import set_sender_ctx, get_sender_ctx
         >>> driver = SessionContext().with_python_udf_inlining(enabled=False)
         >>> set_sender_ctx(driver)
         >>> get_sender_ctx() is driver
         True
-        >>> clear_sender_ctx()
     """
     _local.sender_ctx = ctx