[WebAssembly][NFC] simplify SjLj inline assembly test

Summary:
Per feedback in D64115, simplify the test.

`hidden` is left in though, because every test in the file has it.

Reviewers: aheejin, tlively

Subscribers: dschuff, sbc100, jgravelle-google, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64117

llvm-svn: 365089