[RONs] Exclude Strikethrough

This CL excludes Strikethrough from Live Updates because text meaning can change when the notification is demoted.

Bug: 430343270
Flag: android.app.ui_rich_ongoing
Test: manual (post a RON with Strikethrough and confirm that this notification does not render Strikethrough)
Change-Id: Ib18069efcde01597bb34ff74dd32c266bc3d300d