Remove unnecessary use of Runtime.getNativeFieldSize. NFC (#15234)

Author: sbc100

src/parseTools.js

@@ -480,7 +480,7 @@ function checkSafeHeap() {
 }
 
 function getHeapOffset(offset, type) {
-  if (Runtime.getNativeFieldSize(type) > 4 && type == 'i64') {
+  if (type == 'i64') {
     // we emulate 64-bit integer values as 32 in asmjs-unknown-emscripten, but not double
     type = 'i32';
   }

src/runtime.js

@@ -46,9 +46,9 @@ function getNativeTypeSize(type) {
 var Runtime = {
   getNativeTypeSize: getNativeTypeSize,
 
-  //! Returns the size of a structure field, as C/C++ would have it (in 32-bit,
-  //! for now).
-  //! @param type The type, by name.
+  //! TODO(sbc): This function is unused by emscripten but we can't be
+  //! sure there are not external users.
+  //! See: https://github.com/emscripten-core/emscripten/issues/15242
   getNativeFieldSize: function(type) {
     return Math.max(getNativeTypeSize(type), Runtime.QUANTUM_SIZE);
   },