Revert "Add controller for magnification feedback preference"

This reverts commit 3f677476.

Reason for revert: This change was reverted to accommodate a design
update. The display of hats has been moved to a menu action, as
detailed in the new design specification ag/32298200.

Bug: 380346799
Test: Manual testing on Pixel and non-Pixel devices
Flag: com.android.server.accessibility.enable_low_vision_hats
Change-Id: Ide42f033248598cb1b9f0d6f0f95de2ff6690866