sched_yield: delete sysctl_sched_compat_yield

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

If echo "1">/proc/sys/kernel/sched_compat_yield before starting volanoMark
testing, the result is very good with kernel 2.6.24-rc3 on my 16-core tigerton.

1) If /proc/sys/kernel/sched_compat_yield=1, comparing with 2.6.22,
2.6.24-rc3 has more than 70% improvement;
2) If /proc/sys/kernel/sched_compat_yield=0, comparing with 2.6.22,
2.6.24-rc3 has more than 80% regression;

On other machines, the volanoMark result also has much improvement if
/proc/sys/kernel/sched_compat_yield=1.

Would you like to change function yield_task_fair to delete codes around
sysctl_sched_compat_yield, or just initiate it to 1?

Thanks,
Yanmin