Handles Flash Notifications intro if there's no valid camera

If there is no valid camera found on the device, the camera flash option will be hidden by default. It seems weired if the intro still mentions the camera light will flash while there's no camera flash option at all. Updates the intro string without mentioning camera light if there's no valid camera found.

Bug: 274565006
Test: check the string on device without valid camera manually
Change-Id: I93b1fe372fe9f9e2634e56b19b30898847d68c9c