Changes

releng: Remove non-release plug-in/fragments from 9.1.0 baseline

The callstack plug-ins are still in development and not provided on the
Trace Compass update site. Also, the fragment for slf4j properties is
not on the update site.

Change-Id: If6086f12971012860dfccdd98b347a5587ebeda1
Signed-off-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/203428
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>