ENG-7274: Eliminate the deprecated 'groups' attribute in the user

element in the deployment file.
- Clean up some code that merged both
- Clean up a bunch of other code that used 'group' instead of 'role',
mostly in test code.
- Remove redundant code from RealVoltDB and clean up
I was torn between leaving it as is and detecting and adding it if it's missing in compileDeployment, but that felt like something outside of compileDeployment's purview.