tmf: Mark ITmfEventRequest.handleData's parameter as NonNull

tmf: Mark ITmfEventRequest.handleData's parameter as NonNull

It seems every single event request implementation out there does
a null check on the event it receives in handleData(). TmfEventThread
already does a null check before sending the event to this method,
so it can be marked @NonNull, which avoids a bunch of redundant checks.

Change-Id: I1d54d5f3f5a08af150ab0a6011d075a366db4b48
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/26247
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>