ephemeral: clear more fields in delete_expired_messages

These fields are cleared in other places,
but in the case of delete_device_after setting
only txt column was cleared previously.

src/ephemeral.rs

@@ -378,7 +378,8 @@ WHERE
             .sql
             .execute(
                 "UPDATE msgs \
-             SET txt = 'DELETED', chat_id = ? \
+             SET chat_id = ?, txt = '', subject='', txt_raw='', \
+                 mime_headers='', from_id=0, to_id=0, param='' \
              WHERE timestamp < ? \
              AND chat_id > ? \
              AND chat_id != ? \