Remove torrent checking for channel torrents

[xoriole]

This PR removed the torrent checks on torrents of the user channel. Since channels are removed, it does not make sense to keep these checks anymore. Besides, for a large metadata database (~5GB), the query to select torrent from user channel is pretty slow (161.362 seconds). See log below.

[tribler-core PID:10196] 2024-02-02 23:21:52,505 - WARNING - tribler.core.utilities.pony_utils(268) - Long db_session detected.
Session info:
    Thread: 'MainThread'
    db_session duration: 161.362 seconds
    db_session waited for the exclusive lock for 0.000 seconds
    db_session held exclusive lock for 0.000 seconds
The db_session stack:
  File "C:\Users\tribler\PycharmProjects\tribler\venv8\lib\site-packages\ipv8\taskmanager.py", line 25, in interval_runner
    await task(*args)
  File "C:\Users\tribler\PycharmProjects\tribler\src\tribler\core\components\torrent_checker\torrent_checker\torrent_checker.py", line 266, in check_torrents_in_user_channel
    selected_torrents = self.torrents_to_check_in_user_channel()

Queries statistics for the current db_session:
1 query executed in a total of 161.358 seconds;
The slowest query (161.358 seconds) is:
    SELECT "g"."rowid", "g"."infohash", "g"."size", "g"."torrent_date", "g"."tracker_info", "g"."title", "g"."tags", "g"."metadata_type", "g"."reserved_flags", "g"."origin_id", "g"."public_key", "g"."id_", "g"."timestamp", "g"."signature", "g"."added_on", "g"."status", "g"."xxx", "g"."health", "g"."tag_processor_version"
    FROM "ChannelNode" "g", "TorrentState" "torrentstate"
    WHERE "g"."metadata_type" IN (300)
      AND "g"."public_key" = ?
      AND "g"."metadata_type" = ?
      AND "torrentstate"."last_check" < ?
      AND "g"."health" = "torrentstate"."rowid"
    ORDER BY "torrentstate"."last_check"
    LIMIT 5
    ```