Python: Fix bad join order for `global_name_used`.
Python: Fix bad join order for `global_name_used`.

As it turns out, there was a further bad join-order in the `global_name_used`
predicate. In this case, there was a common subexpression in the RA that was
being factored out and evaluated separately, producing a large number of tuples.

github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql,github/codeql