critical path: bug 494196 reset selection when trace selected

critical path: bug 494196 reset selection when trace selected

This resets the selection in the parameter provider so that if a thread is
selected again in the control flow view, the selection change is triggered
again.

Change-Id: I92f4203d0181f996efcbc2618c32d35311761003
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/73318
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>