ext4: remove conflicting comment from __ext4_forget

We do a bforget and return for no journal case, so let's remove this
conflict comment.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
Link: https://lore.kernel.org/r/20210714055940.1553705-1-guoqing.jiang@linux.dev
Signed-off-by: Theodore Ts'o <tytso@mit.edu>