[OutputBuilder] Add basic functionality for removing individual combination groups from rule RHS.
[OutputBuilder] Add basic functionality for removing individual
combination groups from rule RHS.

Note that we don't do any real error handling yet, and that group
positions do not get updated when deleting any group other than the last
one (i.e., the one with the highest "position" value).

itsjeyd/ODE,itsjeyd/ODE,itsjeyd/ODE,itsjeyd/ODE