sched: clean up fastcall uses of sched_fork()/sched_exit()

sched_fork()/sched_exit() does not need to specify fastcall anymore,
as the x86 kernel defaults to regparm3, and no assembly code calls
these functions.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --cc include/linux/sched.h
Simple merge