Don't set the app launcher icon as the icon for implicit rules

And clear it from existing rules.

Many app icons don't have a monochrome variant, and even when they do they might not be appropriate for some surfaces where mode icons are displayed. Instead, use a default icon (which the user can customize, if they want).

Should be ok to change since it wasn't visible anywhere before MODES_UI.

Flag: android.app.modes_ui
Fixes: 361597532
Test: atest ZenModeHelperTest
Change-Id: I47d8b132287ffc50a74316898c2071fbb31e13ed