Deprecate "phone_switching_supported" key in Settings Provider

This change deprecates the key "phone_switching_supported" in
Settings Provider and all its usages since it is now defaulted to
true.
Flag: EXEMPT for code removal
Bug: 352123885
Test: Manual

Change-Id: I4f8f932987a71c0114c3ed86a751fd40a275d196
3 files changed