[WebAssembly] Remove premature optimization.

[ruiu]

Summary

I think calling reserve() for each object file is too many and isn't useful.
We can add reserve() later. By default, we shouldn't add reserve() to a lot
of places.

lld/wasm/Writer.cpp

 }
 
 // Populate InitFunctions vector with init functions from all input objects.
 // This is then used either when creating the output linking section or to
 // synthesize the "__wasm_call_ctors" function.
 void Writer::calculateInitFunctions() {
   for (ObjFile *File : Symtab->ObjectFiles) {
     const WasmLinkingData &L = File->getWasmObj()->linkingData();
-    InitFunctions.reserve(InitFunctions.size() + L.InitFunctions.size());
     for (const WasmInitFunc &F : L.InitFunctions)
       InitFunctions.emplace_back(
           WasmInitEntry{File->getFunctionSymbol(F.Symbol), F.Priority});
   }
+
   // Sort in order of priority (lowest first) so that they are called
   // in the correct order.
   std::stable_sort(InitFunctions.begin(), InitFunctions.end(),
                    [](const WasmInitEntry &L, const WasmInitEntry &R) {
                      return L.Priority < R.Priority;
                    });
 }