Fix redundant cast in class merging policy

Change-Id: Ida3ef8460f6a4480823ebd192b9f7e32aad6570e

src/main/java/com/android/tools/r8/horizontalclassmerging/policies/PreventMergeIntoMainDex.java

diff --git a/src/main/java/com/android/tools/r8/horizontalclassmerging/policies/PreventMergeIntoMainDex.java b/src/main/java/com/android/tools/r8/horizontalclassmerging/policies/PreventMergeIntoMainDex.java
index da65126..f17e923 100644
--- a/src/main/java/com/android/tools/r8/horizontalclassmerging/policies/PreventMergeIntoMainDex.java
+++ b/src/main/java/com/android/tools/r8/horizontalclassmerging/policies/PreventMergeIntoMainDex.java
@@ -43,8 +43,7 @@
 
     Collection<Collection<DexProgramClass>> newGroups = new LinkedList<>();
     if (!isTrivial(mainDexMembers)) {
-      // TODO(b/165577835) remove this cast when we introduce MergeGroup.
-      newGroups.add((Collection) mainDexMembers);
+      newGroups.add(mainDexMembers);
     }
     if (!isTrivial(group)) {
       newGroups.add(group);