Allow dispatcher to be idle after metrics push

Earlier, the dispatcher was not being allowed to enter idle state
since processLatencyStatisticsLocked() would always wake it up in 6 hours,
causing many of the dispatcher tests to fail.
Now, the dispatcher will be idle after the latency statistics are
pushed. After the statistics push is complete, the next push will occur
after 6 hours upon the next input event being received by the
dispatcher.

Bug: 270049345
Test: atest inputflinger_tests
Flag: com.android.input.flags.enable_per_device_input_latency_metrics
Change-Id: I1cdb6df6110bff9e4fcb6cbfdc91c16c8e386f0b