The API for review request drafts was allowing target_groups to match up

group display names. This was here for old legacy reasons, but is

undocumented, and it's very unlikely anyone is making use of it anymore.

(If they are, they'll have to adapt.)
The main reason this was a problem was that a group could have a display

name matching another group's ID, which would result in an error in

adding that group. That case was confusing and non-obvious, and worth

making the above change.

Unit tests pass.
Tested adding a group with an ID matching another group's display name.

Didn't hit any problems after this change.