Revert "SystemUI: Add support for clock auto-hiding"

This reverts commit 7c39df7c.

Reason for the revert: It has bugs and will be implemented differently
without messing up with AOSP code.

Steps to reproduce clock visibility issues:

 - Enable auto-hide feature
 - Go to home screen (clock will hidden) ✅
 - Open any app (clock will appear) ✅
 - Lock device and notice that clock will show up in the statusbar ❌

Change-Id: I6946c10b670807f47eb6c9d2e735d2f675ed7fd7