[lld][WebAssembly] Don't force the export symbols assiged internal/dummy GOT entries

Symbols with regular GOT entries do need to be exported, but those that
are internalized (and have dymmy/internal GOT entries) need not be
exported.

This happens to fix the failures on the emscripten waterfall where extra
symbols were being exported by the linker (and then later removed by
wasm-opt).

Differential Revision: https://reviews.llvm.org/D119902