Deprecate cbook.report_memory.

It's unrelated to Matplotlib's functionality, and more importantly it
likely never worked on Py3 (currently raising "'int' object has no
attribute 'split'") because the subprocess needs to be called with
`universal_newlines=True`, otherwise (currently) stdout is returned as
bytes and indexing that gives an int, not a str...

Author: anntzer

doc/api/next_api_changes/deprecations/20209-AL.rst

@@ -0,0 +1,3 @@
+``cbook.report_memory``
+~~~~~~~~~~~~~~~~~~~~~~~
+... is deprecated.  Use ``psutil.virtual_memory`` instead.

lib/matplotlib/cbook/__init__.py

@@ -628,6 +628,7 @@ def remove(self, o):
                 self.push(elem)
 
 
+@_api.deprecated("3.5", alternative="psutil.virtual_memory")
 def report_memory(i=0):  # argument may go away
     """Return the memory consumed by the process."""
     def call(command, os_name):