Exclude implicit modes from the summary of the Modes entry in Settings

They are called "Do Not Disturb (App)" which places alphabetically near the top (in English). This can often result in a summary like "DND, Bedtime, DND (App)", which looks silly.

Fixes: 379089451
Test: atest ZenModeSummaryHelperTest
Flag: android.app.modes_ui
Change-Id: Id41caee09cca874297ca12d2ac934aed3f9a43ab