[OutputBuilder] Remove "Add group" button from current group when inserting new group.
[OutputBuilder] Remove "Add group" button from current group when
inserting new group.

Since groups are always added at the bottom, for now we only show the
"Add group" button on the latest (bottom) group.

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