Remove references to OMERO.editor

OMERO.editor is being removed for 5.1. This removes references to it from the docs.

--no-rebase

Only other page referencing it is http://www.openmicroscopy.org/site/support/omero5.1/developers/Insight/ImplementationView.html which i looked at and then wondered if the entire thing was out-of-date @jburel ?