Delete PanelView

Pushed all of PanelView's members down into NotificationPanelView
and replaced all of PanelView's references using IntelliJ.
Checked usage of everything and reduced visibility where possible,
inlined constants used only once, and deleted dead code.

Fixes: 242211739
Test: atest SystemUITests SystemUIGoogleTests
Change-Id: I6e799cf791b63e8acf178df7e81d8a39de654e84