Removes test_force_delete_server_invalid_state negative test

Commit I06a476701ccb47d8f7fd6e43c394ccb3fac2b3aa allows the force
deleting of running instances as well as those in soft-delete state
so this negative test is no longer appropriate.

Related-Bug: #1351001
Change-Id: Ia6d09fea753196a8bc9f33ac8acaae49f1d306e7
diff --git a/tempest/api/compute/servers/test_servers_negative.py b/tempest/api/compute/servers/test_servers_negative.py
index 792b523..b9ec29e 100644
--- a/tempest/api/compute/servers/test_servers_negative.py
+++ b/tempest/api/compute/servers/test_servers_negative.py
@@ -404,13 +404,6 @@
                           nonexistent_server)
 
     @test.attr(type=['negative', 'gate'])
-    def test_force_delete_server_invalid_state(self):
-        # we can only force-delete a server in 'soft-delete' state
-        self.assertRaises(exceptions.Conflict,
-                          self.client.force_delete_server,
-                          self.server_id)
-
-    @test.attr(type=['negative', 'gate'])
     def test_restore_nonexistent_server_id(self):
         # restore-delete a non existent server
         nonexistent_server = data_utils.rand_uuid()