docs: Don't include ChangeLog

The ChangeLog is built using commit message summary lines. Unfortunately
some of these contain invalid rST markup. There's no way to
retroactively fix this, so simply stop including the doc.

Change-Id: I6600c1baf142fe4c776f1ae170faa3f6a87b330c

Author: stephenfin

doc/source/history.rst

@@ -43,7 +43,6 @@ Release Notes
    :maxdepth: 1
 
    Release Notes <http://docs.openstack.org/releasenotes/python-openstackclient>
-   history
 
 Developer Documentation
 -----------------------