[pvr] isolate and reuse the code that sets the last watched status for channels
[pvr] use m_addons directly, no need to use the getter here
[pvr] remove a lot of unused methods
[pvr] don't queue the channel switch manually, reuse the method for it
[pvr] don't remove a pending job from the queue until it has been
completed, otherwise we may unnecessarily queue similar jobs
[pvr] remove lock that shouldn't be there
[pvr] remove unneeded lock