Handle OnCall gateway connector delete 204 (#1313)

Deleting an oncall connector from the gateway returns a 204 so it should
not try to parse the response for json.

.github/ISSUE_TEMPLATE/issue-template.md

@@ -10,6 +10,7 @@ assignees: ''
 Hi, thank you for opening an issue!
 
 Here is a quick checklist:
+
 - [ ] Is it about Cloud or Open Source OnCall?
 - [ ] Add OnCall backend & frontend versions.
 - [ ] Include labels starting with "part:". Like `part:alertflow` or `part:schedules`.

engine/common/oncall_gateway/oncall_gateway_client.py

@@ -52,14 +52,7 @@ class OnCallGatewayAPIClient:
     def delete_oncall_connector(self, oncall_org_id: str) -> requests.models.Response:
         url = urljoin(f"{self._oncall_connectors_url}/", oncall_org_id)
         response = self._delete(url=url)
-        response_data = response.json()
-        return (
-            OnCallConnector(
-                response_data["oncall_org_id"],
-                response_data["backend"],
-            ),
-            response,
-        )
+        return response
 
     # Slack Connector
     @property