[WebAssembly] Remove flags from MCSectionWasm

Looks like these were copied from the ELF sections but
don't apply to Wasm and were not used anywhere.

Also remove unused Wasm methods in MCContext.

Differential Revision: https://reviews.llvm.org/D37633

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313058 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed