Remove sheepdog tests from zuul config

The sheepdog project is no longer maintained [0], so this removes the
test configuration as part of an effort to clean up those test
definitions. The glance_store support for sheepdog should also be
deprecated and removed, but that will be done separately.

[0] http://lists.wpkg.org/pipermail/sheepdog/2019-March/068451.html

Change-Id: I79d9dbc8f6ebea381d99e96c4ba4194ba0188b8a
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>
(cherry picked from commit a7a6064e7d)

.zuul.yaml

@@ -170,11 +170,6 @@
             irrelevant-files:
               - ^(test-|)requirements.txt$
               - ^setup.cfg$
-        - legacy-tempest-dsvm-full-sheepdog:
-            voting: false
-            irrelevant-files:
-              - ^(test-|)requirements.txt$
-              - ^setup.cfg$
     experimental:
       jobs:
         - glance_store-dsvm-functional-filesystem