btrfs-progs: mkfs: Don't use custom chunk allocator for rootdir

btrfs-progs: mkfs: Don't use custom chunk allocator for rootdir

Remove the custom chunk allocator for mkfs. It is buggy in connection to
the --rootdir option and puts file data to the reerved 1M area. The
feature of the custom allocator was to reserve only minimal amount of
blockgroup space. This will temporarily stop working and will need an
explicit request by option, added by following patches.

Use the generic chunk allocator.

Signed-off-by: Qu Wenruo <wqu@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>