Revert "[coroutines][PR40978] Emit error for co_yield within catch block"

The commit https://reviews.llvm.org/rC356296 is causing a regression in nested
catch scopes, https://bugs.llvm.org/show_bug.cgi?id=41171. Revert this change
for now in order to un-break that problem report.

llvm-svn: 356774