Improve Scene launch mode

app/src/main/java/com/hippo/scene/Announcer.java

@@ -23,7 +23,6 @@ public final class Announcer {
     Class<?> clazz;
     Bundle args;
     TransitionHelper tranHelper;
-    int flag;
     SceneFragment requestFrom;
     int requestCode;
 
@@ -41,11 +40,6 @@ public final class Announcer {
         return this;
     }
 
-    public Announcer setFlag(int flag) {
-        this.flag = flag;
-        return this;
-    }
-
     public Announcer setRequestCode(SceneFragment requestFrom, int requestCode) {
         this.requestFrom = requestFrom;
         this.requestCode = requestCode;