s390/sclp: remove orphaned sclp_set_columns and sclp_set_htab

sclp_set_columns and sclp_set_htab are leftovers since commit 095761d2
("[S390] sclp_tty: remove ioctl interface."), remove them as a dead code.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>