Remove obsolete redhat-eventlet.patch

See I62ce43a330d7ae94eda4c7498782a655e63747fa for the gorey details on
why this exists.

As of this fix:

  https://github.com/eventlet/eventlet/pull/34

which was released in eventlet 0.13, we no longer need the patch.

This has now been removed from oslo-incubator, so this is really just
syncing that removal.

Change-Id: I84267f3c6726cb2e750f615e107c48b12c6ed353