ARM: Remove temporary sched_clock.h header

This header file is no longer needed now that the ARM sched_clock
framework is generic and all users have moved to linux/sched_clock.h
instead of asm/sched_clock.h. Remove it.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kevin Hilman <khilman@linaro.org>