Remove AUTHORS

AUTHORS isn't really relevant in the days of git.  devstack has no
formal release where it would make sense to auto-generate an AUTHORS
file either.

If you really want to see who contributes, you can run

 $ git log --format='%aN <%aE>' | sort -f | uniq > AUTHORS

Change-Id: I9e154f7fdf814b4bd21a9d4cf82e46ec3db2f1ca

Author: ianw

.mailmap

@@ -4,3 +4,4 @@
 Jiajun Liu <jiajun@unitedstack.com> <iamljj@gmail.com>
 Jian Wen <jian.wen@canonical.com> <wenjianhn@gmail.com>
 Joe Gordon <joe.gordon0@gmail.com> <jogo@cloudscaling.com>
+Sean Dague <sean.dague@samsung.com> <sdague@linux.vnet.ibm.com> <sean@dague.net>