tmf: Cleanup TmfEventProvider

tmf: Cleanup TmfEventProvider

* Move the fDataQueue, as well as the whole concept of queue size, to
  the test stub. it was only used by that.
* Make some protected fields private.
* Change the ArrayList of pending requests to a linked list. We never
  access a specific index directly, and insertions are faster in a
  linked list.
* Remove fireRequest() from the interface, it should only be used
  internally.
* Remove queueBackgroundRequest(), it's not used anymore (this also
  removes the need for the dispatchRequest() method).

Change-Id: Ie9d2706f90d0afec1b01a35f2684c00eb83217fe
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/20911
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>