Add deleted_branch table fixture (#2832)

* Add deleted_branch table fixture

* Fix deleted branches tests

* Remove unneeded global variable

models/fixtures/deleted_branch.yml

@@ -0,0 +1,15 @@
+-
+  id: 1
+  repo_id: 1
+  name: foo
+  commit: 1213212312313213213132131
+  deleted_by_id: 1
+  deleted_unix: 978307200
+
+-
+  id: 2
+  repo_id: 1
+  name: bar
+  commit: 5655464564554545466464655
+  deleted_by_id: 99
+  deleted_unix: 978307200