remove highlight/group entries from group_by traces since they're redundant now

[pgbovine]

We no longer need group_by's to emit highlight entries in mappings with group IDs, since the group_data field has all of this information already. i'm currently ignoring all these entries in my canonicalization script, so it would be nice later on to just not generate them in the first place:

        {
          "type": "highlight",
          "target": {
            "table": "rhs",
            "row": 3,
            "col": "all"
          },
          "group": 2
        },