Use the UNIMPLEMENTED macro everywhere.

As suggested in review.

Change-Id: Ic14c91a622b545b4800ef021dfb501fb09cbda9d
diff --git a/src/class_linker.cc b/src/class_linker.cc
index 4522378..4524457 100644
--- a/src/class_linker.cc
+++ b/src/class_linker.cc
@@ -865,7 +865,7 @@
   } else {
     // JValue unused;
     // TODO: dvmCallMethod(self, method, NULL, &unused);
-    //CHECK(!"unimplemented");
+    // UNIMPLEMENTED(FATAL);
   }
 
   {