dont unbind header text so the view can be fade out in transition.

This is because we changed from removeView to recycleView when layout is disabled.
However we still want to use the recycled view during transition.

b/15417457

Change-Id: Ia499176117688e644edfba0030b112ea0a79585c
diff --git a/v17/leanback/src/android/support/v17/leanback/widget/RowHeaderPresenter.java b/v17/leanback/src/android/support/v17/leanback/widget/RowHeaderPresenter.java
index 2479420..886bf89 100644
--- a/v17/leanback/src/android/support/v17/leanback/widget/RowHeaderPresenter.java
+++ b/v17/leanback/src/android/support/v17/leanback/widget/RowHeaderPresenter.java
@@ -81,7 +81,6 @@
 
     @Override
     public void onUnbindViewHolder(Presenter.ViewHolder viewHolder) {
-        ((RowHeaderView) viewHolder.view).setText(null);
     }
 
     public final void setSelectLevel(ViewHolder holder, float selectLevel) {