Get rid of JSExitStub which is no longer used anywhere.

src/code-stubs.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 114 matching lines @@
     case CEntry:
       return "CEntry";
     case JSEntry:
       return "JSEntry";
     case GetProperty:
       return "GetProperty";
     case SetProperty:
       return "SetProperty";
     case InvokeBuiltin:
       return "InvokeBuiltin";
-    case JSExit:
-      return "JSExit";
     case ConvertToDouble:
       return "ConvertToDouble";
     case WriteInt32ToHeapNumber:
       return "WriteInt32ToHeapNumber";
     default:
       UNREACHABLE();
       return NULL;
   }
 }
 
 
 } }  // namespace v8::internal