[lld][WebAssembly] Revert moving of data relocations to start function

Back in https://reviews.llvm.org/D117412 we moved the application of
data reloctions to the wasm start function.

However, because the dynamic linker doesn't know the final addresses
at module instantiation time, this proved to be too early and the
relocations could be applied with the wrong values.

Fixes: https://github.com/emscripten-core/emscripten/issues/17150

Differential Revision: https://reviews.llvm.org/D127333