Fix port script for user directory tables

scripts/synapse_port_db

@@ -252,6 +252,24 @@ class Porter(object):
             )
             return
 
+        if table in (
+            "user_directory", "user_directory_search", "users_who_share_rooms",
+            "users_in_pubic_room",
+        ):
+            # We don't port these tables, as they're a faff and we can regenreate
+            # them anyway.
+            self.progress.update(table, table_size)  # Mark table as done
+            return
+
+        if table == "user_directory_stream_pos":
+            # We need to make sure there is a single row, `(X, null)`
+            yield self.postgres_store._simple_insert(
+                table=table,
+                values={"stream_id": None},
+            )
+            self.progress.update(table, table_size)  # Mark table as done
+            return
+
         forward_select = (
             "SELECT rowid, * FROM %s WHERE rowid >= ? ORDER BY rowid LIMIT ?"
             % (table,)