Revert "Add an overlayable config for IME switcher visibility."

This reverts commit fa0e47e0 [1].

Reason for revert: This config is no longer used.

 [1]: Id2aef6597916422ea63435ae9c31a9a9b5ddf5b8

Bug: 26245853
Fix: 135747008
Test: compile
Change-Id: Icdf65be5ddc47fbb8dab225654bad234f16ca644