Remove more dead code after Object.observe removal

src/runtime/runtime-function.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/compiler.h"
 #include "src/frames-inl.h"
@@ skipping 262 matching lines @@
       Execution::Call(isolate, target, receiver, argc, argv.start()));
   return *result;
 }
 
 
 // ES6 section 9.2.1.2, OrdinaryCallBindThis for sloppy callee.
 RUNTIME_FUNCTION(Runtime_ConvertReceiver) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, receiver, 0);
-  if (receiver->IsNull() || receiver->IsUndefined()) {
-    return isolate->global_proxy();
-  }
-  return *Object::ToObject(isolate, receiver).ToHandleChecked();
+  return *Object::ConvertReceiver(isolate, receiver).ToHandleChecked();
 }
 
 
 RUNTIME_FUNCTION(Runtime_IsFunction) {
   SealHandleScope shs(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_CHECKED(Object, object, 0);
   return isolate->heap()->ToBoolean(object->IsFunction());
 }
 
 
 RUNTIME_FUNCTION(Runtime_FunctionToString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_ARG_HANDLE_CHECKED(JSReceiver, function, 0);
   return function->IsJSBoundFunction()
              ? *JSBoundFunction::ToString(
                    Handle<JSBoundFunction>::cast(function))
              : *JSFunction::ToString(Handle<JSFunction>::cast(function));
 }
 
 }  // namespace internal
 }  // namespace v8