Revert "Sema: fix comparison with undefined"

This reverts commit 547481c31c8a538a7badbdce66d81820177ce87f.

There is a comment that did not get addressed with this patch, and the
required test cases are not added.

Reopens #17798.
70d8baaec1Andrew Kelley committed on 11/12/2023, 9:33:17 PMparent7048e93
2 files changedLine totals unavailable