Revert r304117 - WebAssembly object format isn't ready to be the default
Summary: Wasm object format has some functionality regressions from the ELF format, and doesn't play nicely with the rest of the toolchain. It should eventually be the default, but not yet.
Reviewers: sunfish, sbc100
Subscribers: jfb, dschuff, llvm-commits
Differential Revision: https://reviews.llvm.org/D33811