tmf: Don't use ITmfEventField in TmfEventsTable

tmf: Don't use ITmfEventField in TmfEventsTable

TmfEventsTable used ITmfEventFields to transfer what it calls
the "fields" of an event row in the table. These are simple Strings
at their heart though, ITmfEventField is used for event payloads only.

This removes many unnecessary object creations.

Change-Id: Ieb82651c6dc7b54505e24a1c21cfa3222a193bbf
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/26231
Tested-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>