[WebAssembly] Remove unneeded MCSymbolRefExpr variants

We record the type of the symbol (event/function/data/global) in the
MCWasmSymbol and so it should always be clear how to handle a relocation
based on the symbol itself.

The exception is a function which still needs the special @TYPEINDEX
then the relocation contains the signature rather than the address
of the functions.

Differential Revision: https://reviews.llvm.org/D58472

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354697 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed