fix_unreads: Remove dead duplicate build_topic_unmute_checker.

The only caller for this function, which is part of a very old
migration, was removed in b77da6b834.

zerver/lib/fix_unreads.py

@@ -19,36 +19,6 @@ logger = logging.getLogger("zulip.fix_unreads")
 logger.setLevel(logging.WARNING)
 
 
-def build_topic_mute_checker(
-    cursor: CursorWrapper, user_profile: UserProfile
-) -> Callable[[int, str], bool]:
-    """
-    This function is similar to the function of the same name
-    in zerver/lib/topic_mutes.py, but it works without the ORM,
-    so that we can use it in migrations.
-    """
-    query = SQL(
-        """
-        SELECT
-            recipient_id,
-            topic_name
-        FROM
-            zerver_usertopic
-        WHERE
-            user_profile_id = %s
-    """
-    )
-    cursor.execute(query, [user_profile.id])
-    rows = cursor.fetchall()
-
-    tups = {(recipient_id, topic_name.lower()) for (recipient_id, topic_name) in rows}
-
-    def is_muted(recipient_id: int, topic: str) -> bool:
-        return (recipient_id, topic.lower()) in tups
-
-    return is_muted
-
-
 def update_unread_flags(cursor: CursorWrapper, user_message_ids: List[int]) -> None:
     query = SQL(
         """