variability: remove dependency on the tracing plugin

[sergej-koscejev]

Use direct string editor hint to avoid dragging in the tracing plugin with its potentially slow conditional editors.

[sergej-koscejev]

This PR includes #1633 which should be merged first.

[kbirken]

This PR is a follow-up for #1621. The goal of the previous PR was to switch off three hints in FeatureModelConfiguration:

• two hints related to condititional editor
• one hint related to IETS3Tracing

This required a reference to the corresponding hints in order to switch them off. However, some customers want to avoid dependencies to the IETS3Tracing feature, as it slows down their applications. Thus, this PR replaces the reference to the IETS3Tracing hint by a string.

[kbirken]

The new solution how to switch off the IETS3Tracing hint by a string is somewhat brittle. But this is a simple solution for a customer problem, so it is fine. Indeed, it was weird before that a dependency to something had to be added just to switch it off (also on the level of deployed plugins).