Remove indexes for FK (EE)

ee/db/migrate/20181105122803_add_missing_indexes_for_foreign_keys_ee.rb

@@ -21,6 +21,19 @@ class AddMissingIndexesForForeignKeysEE < ActiveRecord::Migration
   end
 
   def down
-    # no-op
+    # MySQL requires index for FK,
+    # thus removal of indexes does fail
+    return if Gitlab::Database.mysql?
+
+    remove_concurrent_index(:application_settings, :file_template_project_id)
+    remove_concurrent_index(:application_settings, :custom_project_templates_group_id)
+    remove_concurrent_index(:board_assignees, :assignee_id)
+    remove_concurrent_index(:board_labels, :label_id)
+    remove_concurrent_index(:ci_pipeline_chat_data, :chat_name_id)
+    remove_concurrent_index(:geo_node_namespace_links, :namespace_id)
+    remove_concurrent_index(:namespaces, :file_template_project_id)
+    remove_concurrent_index(:protected_branch_merge_access_levels, :group_id)
+    remove_concurrent_index(:protected_branch_push_access_levels, :group_id)
+    remove_concurrent_index(:software_license_policies, :software_license_id)
   end
 end