tmf: Add utility method to delete supplementary files of a trace

Add the new (and move an existing) test into a separate file, because
the existing test suite uses the same static traces for all the tests.
If we are to delete a trace's supplementary files, the trace should
be regenerated for other tests!

Change-Id: I0727422dd190d9012e6b8ccce0d7d175711e149b
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Reviewed-on: https://git.eclipse.org/r/82778
Reviewed-by: Hudson CI
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>