GH-61215: threadingmock: Remove unused branch for timeout (#106591)

threadingmock: Remove unused branch for `timeout`

This is no longer needed as the mock does not hold a "timeout"
parameter, the timeout is stored in `_mock_wait_timeout`.

Backports: 3e23fa71f43fb225ca29a931644d1100e2f4d6b8
Signed-off-by: Chris Withers <chris@simplistix.co.uk>

mock/mock.py

@@ -3064,9 +3064,7 @@ class ThreadingMixin(Base):
     DEFAULT_TIMEOUT = None
 
     def _get_child_mock(self, **kw):
-        if "timeout" in kw:
-            kw["timeout"] = kw.pop("timeout")
-        elif isinstance(kw.get("parent"), ThreadingMixin):
+        if isinstance(kw.get("parent"), ThreadingMixin):
             kw["timeout"] = kw["parent"]._mock_wait_timeout
         elif isinstance(kw.get("_new_parent"), ThreadingMixin):
             kw["timeout"] = kw["_new_parent"]._mock_wait_timeout