dm: zoned: Remove unused functions

dmz_resume_metadata() is unused since it was added in commit
3b1a94c8 ("dm zoned: drive-managed zoned block device target")

dmz_zone_nr_blocks_shift is unused since it was added in commit
36820560 ("dm zoned: move fields from struct dmz_dev to dmz_metadata")

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>