sched: kill off dead cfs_rq_set_shares()

Building with CONFIG_FAIR_GROUP_SCHED=y on UP results in an unused
cfs_rq_set_shares() reference. As nothing is using this dummy function
in the first place, just kill it off.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>