[wasm] Remove unneeded i64 to i32 truncation

This is a leftover of the time where the memory size was stored as
64 bit value. Now it is stored as 32 bit value, so no need to truncate.

R=ahaas@chromium.org

Change-Id: I44a1505ebd564aee53e4c9a7168738fcb855264b
Reviewed-on: https://chromium-review.googlesource.com/1034883Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52905}

src/compiler/wasm-compiler.cc

@@ -3571,10 +3571,6 @@ Node* WasmGraphBuilder::CurrentMemoryPages() {
   DCHECK_NOT_NULL(instance_cache_);
   Node* mem_size = instance_cache_->mem_size;
   DCHECK_NOT_NULL(mem_size);
-  if (jsgraph()->machine()->Is64()) {
-    mem_size = graph()->NewNode(jsgraph()->machine()->TruncateInt64ToInt32(),
-                                mem_size);
-  }
   return graph()->NewNode(
       jsgraph()->machine()->Word32Shr(), mem_size,
       jsgraph()->Int32Constant(WhichPowerOf2(wasm::kWasmPageSize)));