Clean up AccessibilitySettings

Since AccessibilitySettings has been converted to DashboardFragment, and
those preference controllers are moved to corresponding xml files which
will be loaded statically, so here we are removing those in-code
preference controllers as we no longer need them.

The following controllers will be removed:
ColorInversionPreferenceController
LockScreenRotationPreferenceController
FontSizePreferenceController
MagnificationPreferenceController

There are still some controllers used here. We will remove them soon
once they are all converted to static ones.

Bug: 135056871
Test: manual, robotests
Change-Id: I7897b984b2275e98f958ad65b576dd08aaab3f06