Deprecate `//sensor/camera/pose`

A camera is the only sensor that allows specifying a pose element on top of `//sensor/pose`. I wonder if there is any utility in this or if it could be depreciated.

I can see how this might be relevant to the idea of specifying that a camera is attached at some position, and origin/center of the lense model has some offset to that. However, I think this case can easily be covered by setting the position of the `//sensor` to that position and introducing a fixed link from the sensor mount to the lense origin. This is likely a more accurate description anyway since the mount point is connected to a rigid body (the camera casing) which itself is attached to the lense system.

@azeey Would I have to write a dedicated proposal for this, or should this live here?