style: remove unused is_async parameter from _prepare_delete_all_request

The is_async parameter is no longer needed since wait_for_completion
is always True for delete_all_documents operations

Author: GunaPalanivel

integrations/opensearch/src/haystack_integrations/document_stores/opensearch/document_store.py

@@ -596,7 +596,7 @@ async def delete_documents_async(
 
         await async_bulk(**self._prepare_bulk_delete_request(document_ids=document_ids, is_async=True, refresh=refresh))
 
-    def _prepare_delete_all_request(self, *, is_async: bool, refresh: bool) -> dict[str, Any]:
+    def _prepare_delete_all_request(self, *, refresh: bool) -> dict[str, Any]:
         return {
             "index": self._index,
             "body": {"query": {"match_all": {}}},  # Delete all documents
@@ -638,7 +638,7 @@ def delete_all_documents(self, recreate_index: bool = False, refresh: bool = Tru
 
             else:
                 result = self._client.delete_by_query(
-                    **self._prepare_delete_all_request(is_async=False, refresh=refresh)
+                    **self._prepare_delete_all_request(refresh=refresh)
                 )
                 logger.info(
                     "Deleted all the {n_docs} documents from the index '{index}'.",
@@ -681,7 +681,7 @@ async def delete_all_documents_async(self, recreate_index: bool = False, refresh
             else:
                 # use delete_by_query for more efficient deletion without index recreation
                 await self._async_client.delete_by_query(
-                    **self._prepare_delete_all_request(is_async=True, refresh=refresh)
+                    **self._prepare_delete_all_request(refresh=refresh)
                 )
 
         except Exception as e: