Multi-root is the only mode in Che-Theia, no feature toggle anymore

[azatsarynnyy]

Is your task related to a problem? Please describe.

Since Che 7.27, there's multi-root layout support in Che-Theia.
For the transition period, we have added a feature toggle in a devfile:

attributes:
 multiRoot: 'on'

It's a default layout in Che-Theia, for the last sprint. We see no more critical issues with that. So, no need to support both layouts anymore.

Describe the solution you'd like

Remove the feature toggle support from Che-Theia.

Describe alternatives you've considered

Additional context

Release notes

This is not a n&n issue but like the end of a deprecation policy
End of the deprecation, now we can't revert to the old mode without multi-root