idle: Remove needless "expired" logic in sys_power_save_idle()
idle: Remove needless "expired" logic in sys_power_save_idle()

This code (just refactored as part of the timer API work) turns out to
be needless.  It's trying to detect the case where we're being asked
to idle for zero time, but that's not possible with a properly
functioning timer driver: the call to z_clock_announce() must happen
out of an interrupt, and this is the idle thread, which must sit below
any possible interrupt priority.  The call to z_clock_uptime() must
not ever return "too late" until after the timer interrupt has fired,
at which point we'll be inspecting the next timeout (which itself is
guaranteed to be in the future for the same reason).

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

ldts/zephyr,ldts/zephyr,ldts/zephyr,punitvara/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,punitvara/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,explora26/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,Vudentz/zephyr