docs(releasing): remove Docker release section
docs(releasing): remove Docker release section

We no longer deploy to docker.doit.wisc.edu and haven't for a long time.
uPortal-Project/uportal-app-framework,UW-Madison-DoIT/uw-frame,uPortal-Project/uportal-app-framework,uPortal-Project/uportal-app-framework,UW-Madison-DoIT/uw-frame,UW-Madison-DoIT/uw-frame