Don't disable APIs which ensure the contrast of system bars

They were disabled if the app is forced to be edge-to-edge. But there
might be risks that some apps might overlook the API change so that they
don't protect the 3-button navigation bar.

This CL takes those APIs back.

Bug: 309578419
Test: presubmit
Change-Id: Ibc1f805bf6bd8c80c76ea33caf094b3cd071af1d