Remove deprecated labeling properties tab if not used by older project

Deprecated labels tab remains active for all layers in an older project, if any layer uses them, for the duration of project's open session

Caveat (feature?):
- If all layers no longer use deprecated labels on project close, when reopened, deprecated labels tab will no longer be available

I created another branch where the deprecated labels tab was only turned on for the layers that use deprecated labels (7eb4866ff38ee1d0e9c8b16dc6921b762e8ba056). However, this was fairly limiting (see commit message) and would probably annoy users.