Remove closure _unshelve_server not useful

The "_unshelve_server" method is not effective since it is executed
after tearDown, as it is scheduled with addCleanup. During the tearDown
process, the "server_check_teardown" method waits for a server to be
in the "ACTIVE" state. If a timeout occurs, the server is destroyed
to create a new one and continue the test safely.

Therefore, either the test exits tearDown with an "ACTIVE" server, in
which case "_unshelve_server" will do nothing since it checks for a
"SHELVED" server, or the server is destroyed upon exiting tearDown,
and "_unshelve_server" raises an exception, as we can see in the
stack trace for issue #2016957.

Related-Bug: #2016967
Change-Id: Id34c82b001c77ba65ae987dc5eb6b925bc1b279f
diff --git a/tempest/api/compute/servers/test_server_actions.py b/tempest/api/compute/servers/test_server_actions.py
index 4049883..e74ff18 100644
--- a/tempest/api/compute/servers/test_server_actions.py
+++ b/tempest/api/compute/servers/test_server_actions.py
@@ -701,12 +701,6 @@
         compute.shelve_server(self.client, self.server_id,
                               force_shelve_offload=True)
 
-        def _unshelve_server():
-            server_info = self.client.show_server(self.server_id)['server']
-            if 'SHELVED' in server_info['status']:
-                self.client.unshelve_server(self.server_id)
-        self.addCleanup(_unshelve_server)
-
         server = self.client.show_server(self.server_id)['server']
         image_name = server['name'] + '-shelved'
         params = {'name': image_name}