ext4: delete invalid comments near mb_buddy_adjust_border

The comment near mb_buddy_adjust_border seems meaningless, just
clear it.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Link: https://lore.kernel.org/r/1601292995-32205-1-git-send-email-brookxu@tencent.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>