Drop non-const interface of IEnvelopeDefSvc
The non-const accessors of IEnvelopeDefSvc were marked for deprecation in 2014. Apparently nobody in the last six years got around to adjust the clients. Even when the clients were migrated to Cond-Algos, the non-const access part was copied over. With this MR, the clients are updated and the not-const interface is removed.
This MR shoudl fix the build-warnings we see since a few days in the master branch.
PS, in case you wonder: IEnvelopDefSvc is not an abstract interface as the name might suggest.