Modify RetraceApi to have @Keep annotation

Change-Id: Ifc21c48128ac29756439f2d6c1f23b809d49cea7
diff --git a/src/main/java/com/android/tools/r8/retrace/RetraceApi.java b/src/main/java/com/android/tools/r8/retrace/RetraceApi.java
index 551dac4..7bb9232 100644
--- a/src/main/java/com/android/tools/r8/retrace/RetraceApi.java
+++ b/src/main/java/com/android/tools/r8/retrace/RetraceApi.java
@@ -4,14 +4,14 @@
 
 package com.android.tools.r8.retrace;
 
-import com.android.tools.r8.KeepForSubclassing;
+import com.android.tools.r8.Keep;
 import com.android.tools.r8.references.ClassReference;
 import com.android.tools.r8.references.FieldReference;
 import com.android.tools.r8.references.MethodReference;
 import com.android.tools.r8.references.TypeReference;
 
 /** This is the main api interface for retrace. */
-@KeepForSubclassing
+@Keep
 public interface RetraceApi {
 
   RetraceMethodResult retrace(MethodReference methodReference);