## Summary
Tracked structs have some issues with fixpoint iteration in Salsa, and
there's not actually any need for this to be tracked, it should be
interned like most of our type structs.
The removed comment was probably never correct (in that we could have
disambiguated sufficiently), and is definitely not relevant now that
`TypeVarInstance` also holds its `Definition`.
## Test Plan
Existing tests.
afc18ff1a1