Hide desktop option from connecion dialog in kiosk mode

When connecting an external display to a device in kiosk mode, we want
to hide the "desktop" option and only allow the device to go into
mirroring.

Bug: 429288575
Flag: com.android.window.flags.enable_updated_display_connection_dialog
Test: ExternalDisplayDialogDelegateScreenshotTest
Change-Id: I3c5eb55d8ef93d2d8a72b685e7ef2a47ceaba2a9