[WebAssembly] Remove unneeded sub-directory

This is the only wasm def (and likely likely will be
for the foreseeable) file so no need for a sub-directory

Differential Revision: https://reviews.llvm.org/D41476

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321246 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed