dm cache: remove remainder of distinct discard block size

Discard block size not being equal to cache block size causes data
corruption by erroneously avoiding migrations in issue_copy() because
the discard state is being cleared for a group of cache blocks when it
should not.

Completely remove all code that enabled a distinction between the
cache block size and discard block size.

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --cc drivers/md/dm-cache-block-types.h
Simple merge

diff --cc drivers/md/dm-cache-metadata.c
Simple merge

diff --cc drivers/md/dm-cache-metadata.h
Simple merge

diff --cc drivers/md/dm-cache-target.c
Simple merge