SF: Remove refresh_rate_switching flag.

ag/9294789 introduce a flag to only allow refresh rate switching on the
devices that have that flag set to true, because it broke devices that
didn't support multiple refresh rates, and Android TV.

LocalDisplayAdapter sets the refresh rate to default when booting the
phone, so no need for that in SF anymore.

Test: Install on devices that doesn't have multiple refresh rates.
Test: Run SF unittests.
Test: Turn on all the flags, and run through set of examples:
      Video playback stays at 60.
      Camera stays at 60.
      Maps play at 60.
      Low brightness stays at 90.
      Swappy successfully switches between 60 & 90.
Test: Turn off all the flags, and rerun the examples from previous.
      If applications requested the change, the change is honored,
      otherwise we stay at default (set by DM).
Test: Ask Android TV team to test the patch.
Bug: 148427603
Change-Id: I44085e91a74902d102bcf9f1491164cdb50650cc