bpo-38916: Document array.array deprecation (GH-17523)

array.array: Document that tostring() and fromstring() deprecated
aliases will be removed in Python 3.9.
(cherry picked from commit 0381ea7)

Co-authored-by: Victor Stinner <[email protected]>

Author: miss-islington

Doc/library/array.rst

@@ -172,6 +172,8 @@ The following data items and methods are also supported:
 
    Deprecated alias for :meth:`frombytes`.
 
+   .. deprecated-removed:: 3.2 3.9
+
 
 .. method:: array.fromunicode(s)
 
@@ -234,6 +236,8 @@ The following data items and methods are also supported:
 
    Deprecated alias for :meth:`tobytes`.
 
+   .. deprecated-removed:: 3.2 3.9
+
 
 .. method:: array.tounicode()