Summary

This PR removes false-positive diagnostics for * imports. Currently we always emit a diagnostic for these statements unless the module we're importing from has a symbol named "*" in its symbol table for the global scope. (And if we were doing everything correctly, no module ever would have a symbol named "*" in its global scope!)

The fix here is sort-of hacky and won't be what we'll want to do long-term. However, I think it's useful to do this as a first step since:

• It significantly reduces false positives when running on code that uses * imports
• It "resets" the tests to a cleaner state with many fewer TODOs, making it easier to see what the hard work is that's still to be done.

Test Plan

cargo test -p red_knot_python_semantic