Remove frame rate flexibility token

Remove the frame rate flexiblity token which can be replaced with

DisplayManager.setRefreshRateSwitchingType(
      DisplayManager.SWITCHING_TYPE_ACROSS_AND_WITHIN_GROUPS);
DisplayManager.setShouldAlwaysRespectAppRequestedMode(true);

Bug: 175371491
Test: m
Change-Id: Ifde95dcdb936e39f894a0ca225ec49f39ca04e62