docs: Removing now-deprecated (and never-used) FLASHLIGHT permission

Per bug b/26383626 , the FLASHLIGHT permission was never actually
used, and isn't checked by the new CameraManager.setTorchMode()
method. The permission has been removed from the manifest on
master; there's no reason to list it now in the list of normal
permissions.

See first comment for doc stage location.

bug: 26383626
Change-Id: I0c39dd5e1cdde1fc6a85759663b7e5ad669dc280