Revert "DateTimeView: Add additional display configuration options."

This reverts commit 66e28940.

Reason for revert: Code no longer needed, using Compose instead

Note that this is a partial revert:
 - It reverts everything in core/ except keeping around the 2 strings
   that are still used by the Compose implementation of this view
 - It does *not* revert everything in packages/SystemUI because those
   changes were still needed by the Compose implementation. The only
   revert in packages/SystemUI is removing the usage of the display
   config options.

Bug: 418250039
Bug: 364653005
Flag: EXEMPT flag removal
Test: atest DateTimeViewTest
Test: Manually verify DateTimeView still functions as it used to
Test: Manually verify new Compose implementation still displays correct relative time strings

Change-Id: I97c02d50b14d814abd235d3b38fb434b3b59cad4