libext2fs: no need to clear BLOCK_UNINIT during ext2fs_reserve_super_and_bgd

libext2fs: no need to clear BLOCK_UNINIT during ext2fs_reserve_super_and_bgd

Since the beginning of the uninit_bg feature, the kernel[1] and
e2fsck[2] have always been careful to detect the presence of the
BLOCK_UNINIT flag, and compute a block bitmap with any group metadata
blocks marked in that bitmap.  With that in mind, I think it's safe to
say that this is a design feature of uninit_bg.

Now that we've trained libext2fs to have this same behavior whenever
it's loading a block bitmap, we no longer need to unset BLOCK_UNINIT
for a group that contains only its own group metadata -- kernel,
e2fsck, and e2fsprogs will handle this correctly.

[1] kernel git 717d50e4971b81b96c0199c91cdf0039a8cb181a
    "Ext4: Uninitialized Block Groups"
[2] e2fsprogs git f5fa20078bfc05b554294fe9c5505375d7913e8c
    "Add support for EXT2_FEATURE_COMPAT_LAZY_BG"

Reported-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>