[cleanup] don't push useless nullptr on ia32/x64 JSEntryStub

The stack value is unused and does not need to be pushed or popped on
return from JSEntryTrampoline

Bug: 
Change-Id: I0e1920fc48b63cb0eea66454e5b74d9b3c2d5956
Reviewed-on: https://chromium-review.googlesource.com/650810
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47849}

src/builtins/ia32/builtins-ia32.cc

@@ -483,7 +483,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
     // context and the function left on the stack by the code
     // invocation.
   }
-  __ ret(kPointerSize);  // Remove receiver.
+  __ ret(0);
 }
 
 void Builtins::Generate_JSEntryTrampoline(MacroAssembler* masm) {

src/builtins/x64/builtins-x64.cc

@@ -560,8 +560,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
     // invocation.
   }
 
-  // TODO(X64): Is argument correct? Is there a receiver to remove?
-  __ ret(1 * kPointerSize);  // Remove receiver.
+  __ ret(0);
 }
 
 void Builtins::Generate_JSEntryTrampoline(MacroAssembler* masm) {

src/ia32/code-stubs-ia32.cc

@@ -672,9 +672,6 @@ void JSEntryStub::Generate(MacroAssembler* masm) {
   __ bind(&invoke);
   __ PushStackHandler();
 
-  // Fake a receiver (NULL).
-  __ push(Immediate(0));  // receiver
-
   // Invoke the function by calling through JS entry trampoline builtin and
   // pop the faked function when we return. Notice that we cannot store a
   // reference to the trampoline code directly in this stub, because the

src/x64/code-stubs-x64.cc

@@ -610,9 +610,6 @@ void JSEntryStub::Generate(MacroAssembler* masm) {
   __ bind(&invoke);
   __ PushStackHandler();
 
-  // Fake a receiver (NULL).
-  __ Push(Immediate(0));  // receiver
-
   // Invoke the function by calling through JS entry trampoline builtin and
   // pop the faked function when we return. We load the address from an
   // external reference instead of inlining the call target address directly