simpleperf: remove code handling cpu hotplug.

cpu hotplug code was disabled in record cmd long time ago, and
becomes obsolete as pixel devices seem no long use cpu hotplug
for thermal control.

Bug: none
Test: run simpleperf_unit_test.
Change-Id: I75fc522792e33afd16dd805ee0c9946ad4a6c67a
3 files changed