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

array.array: Document that tostring() and fromstring() deprecated
aliases will be removed in Python 3.9.

Author: vstinner

Doc/library/array.rst

@@ -173,6 +173,8 @@ The following data items and methods are also supported:
 
    Deprecated alias for :meth:`frombytes`.
 
+   .. deprecated-removed:: 3.2 3.9
+
 
 .. method:: array.fromunicode(s)
 
@@ -235,6 +237,8 @@ The following data items and methods are also supported:
 
    Deprecated alias for :meth:`tobytes`.
 
+   .. deprecated-removed:: 3.2 3.9
+
 
 .. method:: array.tounicode()