Update media deletion after file deletion trigger

Our current trigger is implemented as such:

"CREATE TRIGGER IF NOT EXISTS cascade_file_deletion AFTER DELETE ON "
+ File::Table::Name +
" BEGIN "
" DELETE FROM " + Media::Table::Name + " WHERE "
    "(SELECT COUNT(id_file) FROM " + File::Table::Name +
        " WHERE media_id=old.media_id) = 0"
        " AND id_media=old.media_id;"
" END;",

However, there are multiple assumptions that a Media must have a file of type Main. So we could simplify this trigger by simply removing the media when the removed file type is Main.

This requires a bump in the db model, and should preferably be done once android & iOS get out of the beta period

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