ruff

afc18ff1 - [red-knot] change TypeVarInstance to be interned, not tracked (#17616)

[red-knot] change TypeVarInstance to be interned, not tracked (#17616) ## 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.