[WebAssembly] Misc. fixes in cfg-stackify-eh.ll

- Fix `preds` comments
- Delete nonexistent attributes in instructions (They used to exist in
  clang-generated files, but I removed most of them to make the tests
  tidy. We have only `nounwind` and `noreturn` left here.)
- Add missing `Function Attrs` comments in function declarations

 None of these affect test function semantics or test results for now.

Reviewed By: tlively

Differential Revision: https://reviews.llvm.org/D97179