Remove SampleActor from InstrumentActor. re #9133

As discussed with Roman if ever relevant can be added again
Merge branch 'master' of github.com:mantidproject/mantid into feature/9133_idf_source_shape
Merge remote-tracking branch 'origin/feature/9133_idf_source_shape' into feature/9133_idf_source_shape
Merge branch 'feature/9133_idf_source_shape' into develop