tmf: Merge TmfEventProvider#getType() and ITmfTrace#getEventType()

tmf: Merge TmfEventProvider#getType() and ITmfTrace#getEventType()

TmfTrace has access to both getType() and getEventType(), which
come from two separate super class/interface, but do the exact
same thing.

We can simplify this by only declaring it once, in ITmfEventProvider
(which ITmfTrace extends).

Change-Id: I8a605da5bfd28548d36cd4ce18a1e94d48698176
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/55344
Reviewed-by: Hudson CI