[runtime] Remove the redundant %_IsObject intrinsic.

test/mjsunit/constant-fold-control-instructions.js

Index: test/mjsunit/constant-fold-control-instructions.js
diff --git a/test/mjsunit/constant-fold-control-instructions.js b/test/mjsunit/constant-fold-control-instructions.js
index eb1b0f3c0b70cdc2139c0d59d073b7e1b346342e..a6f5540cfd6dbc92eebf769049d1033a6c3a6e21 100644
--- a/test/mjsunit/constant-fold-control-instructions.js
+++ b/test/mjsunit/constant-fold-control-instructions.js
@@ -12,12 +12,7 @@ function test() {
   assertEquals("function", typeof function() {});
   assertEquals("object", typeof null);
   assertEquals("object", typeof {});
-
-  assertTrue(%_IsObject({}));
-  assertTrue(%_IsObject(null));
-  assertTrue(%_IsObject(/regex/));
-  assertFalse(%_IsObject(0));
-  assertFalse(%_IsObject(""));
+  assertEquals("object", typeof /regex/);
 
   assertTrue(%_IsSmi(1));
   assertFalse(%_IsSmi(1.1));