Remove unused isEmpty method

Change-Id: I5689c55052a3e0bc85c299b57b1ffdd4fbf58612
diff --git a/src/main/java/com/android/tools/r8/optimize/accessmodification/AccessModifierTraversal.java b/src/main/java/com/android/tools/r8/optimize/accessmodification/AccessModifierTraversal.java
index 4922b78..50c7bf7 100644
--- a/src/main/java/com/android/tools/r8/optimize/accessmodification/AccessModifierTraversal.java
+++ b/src/main/java/com/android/tools/r8/optimize/accessmodification/AccessModifierTraversal.java
@@ -136,10 +136,6 @@
     TopDownTraversalState asTopDownTraversalState() {
       return this;
     }
-
-    boolean isEmpty() {
-      return true;
-    }
   }
 
   static class BottomUpTraversalState extends TraversalState {