ext4: remove stale comment in ext4_init_block_bitmap

Commit bdfb6ff4

 ("ext4: mark group corrupt on group descriptor
checksum") added flag to indicate corruption of group instead of
marking all blocks used. Just remove stale comment.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Link: https://lore.kernel.org/r/20230221115919.1918161-6-shikemeng@huaweicloud.com


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