Notify when a display with decorations is removed.

We need to call notifyDisplayRemoveSystemDecorations before
`onDisplayRemoved`.

Fix: 405207598
Flag: com.android.server.display.feature.flags.enable_display_content_mode_management
Test: atest DisplayContentTest
Change-Id: I654bb4428a39fa359c9c1000635dc1c80fb4fdc6