dm persistent data: cleanup dm-thin specific references in text

DM's persistent-data library is now used my multiple targets so
exclusive references to "pool" or "thin provisioning" need to be
cleaned up.  Adjust Kconfig's DM_DEBUG_BLOCK_STACK_TRACING text
and remove "pool" from a block manager error message.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>

diff --cc drivers/md/Kconfig
Simple merge

diff --cc drivers/md/persistent-data/dm-block-manager.c
Simple merge