Cleanup after the interceptor refactoring work, and add a new SSA instruction for an interceptor, s…

sdk/lib/_internal/compiler/implementation/enqueue.dart

Index: sdk/lib/_internal/compiler/implementation/enqueue.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/enqueue.dart	(revision 15190)
+++ sdk/lib/_internal/compiler/implementation/enqueue.dart	(working copy)
@@ -404,11 +404,4 @@
         : 'Compiled ${universe.generatedCode.length} methods.');
     nativeEnqueuer.logSummary(log);
   }
-
-  registerUsedSelector(Selector selector) {
-    Element interceptor = compiler.backend.getInterceptor(selector);
-    if (interceptor != null) {
-      registerStaticUse(interceptor);
-    }
-  }
 }