fix [3176642] Camera preview turns completely black for multiple toggles...

fix [3176642] Camera preview turns completely black for multiple toggles between camera and camcorder app

There was a leak of Surface tokens when a surface was detached from a UserClient.
We now always detach a surface from its client before attaching to the new one,
this guarantees that its token is freed.

Change-Id: Icfad0b16286ed58155bdfafdf36ab161440aa485