Avoid reseting the thread local interner at the beginning of `phase_1_parse_input`
The thread local interner is used before `phase_1_parse_input` to create `InternedString`s, which currently wrap `Rc<String>`s. Once `InternedString` is refactored to be an interned string id (like `Name`), resetting will invalidate everything that was interned before `phase_1_parse_input`.
The resets were only useful for the `rusti` project, which can now use `driver::reset_thread_local_state`.
r? @nrc
29abe5ec71