#17091: update docstring for _thread.Lock.acquire.
#17091: update docstring for _thread.Lock.acquire.

The main docs were fixed to remove mention of None long ago,
but the docstring was not.  Reported by Armin Rigo, patch
by Ian Cordasco.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator