ARM: msm: Remove unused idle.c

Forcing arm_pm_idle to be msm_idle() doesn't make sense in
configurations that don't have CONFIG_MSM7X00A_IDLE=y (i.e. any
targets that aren't 7x00a). Furthermore, that config doesn't even
exist, so this entire file is dead code. Just remove it so we can
use the default idle support on MSM.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>