Remove type hint causing DeprecationWarning in Firestore operators (#…

…9819)

* Import Iterable from collections.abc in firestore operators

DeprecationWarning: Using or importing the ABCs from 'collections'
instead of from 'collections.abc' is deprecated since Python 3.3,
and in 3.9 it will stop working

* Remove the type hint

airflow/providers/google/firebase/operators/firestore.py

@@ -15,7 +15,6 @@
 # specific language governing permissions and limitations
 # under the License.
 
-from collections import Iterable
 from typing import Dict, Optional
 
 from airflow.exceptions import AirflowException
@@ -48,7 +47,7 @@ class CloudFirestoreExportDatabaseOperator(BaseOperator):
     :type api_version: str
     """
 
-    template_fields = ("body", "gcp_conn_id", "api_version")  # type: Iterable[str]
+    template_fields = ("body", "gcp_conn_id", "api_version")
 
     @apply_defaults
     def __init__(