remove disk_name()

Hi Jens,

this series removes the obsolete disk_name helper in favor of using the
%pg format specifier.

Diffstat:
 blk-settings.c    |   12 +++---------
 blk.h             |    1 -
 genhd.c           |   35 +++++++++++++++--------------------
 partitions/core.c |    2 +-
 4 files changed, 19 insertions(+), 31 deletions(-)