Addresses and removes all leftover comments related to the flag overview
redesign flag.
There's four changes here:
1. Remove release plan milestone strategy and environment footer.
Dangling files, no references.
2. Delete old code without references in theme.ts
3. Delete legacy playground result chip. Replace all references to it
with references to the new chip. The API is the exact same and the
legacy chip was just passing through everything to the new chip anyway,
so nothing should change.
4. Remove a now-redundant way to supply a default