BpBinder: remove unused field

Bug: 148177595
Test: atest CompositionSamplingListenerTest
   (broken by other changes in previous CL that included
    this change with other changes, in b/150837217)
Test: boot

Change-Id: I11c9fb7031ae6f226ba279ade9d7ffef7eccb6aa
diff --git a/libs/binder/include/binder/BpBinder.h b/libs/binder/include/binder/BpBinder.h
index 7dca733..93545d7 100644
--- a/libs/binder/include/binder/BpBinder.h
+++ b/libs/binder/include/binder/BpBinder.h
@@ -130,7 +130,6 @@
             volatile int32_t    mObitsSent;
             Vector<Obituary>*   mObituaries;
             ObjectManager       mObjects;
-            Parcel*             mConstantData;
     mutable String16            mDescriptorCache;
             int32_t             mTrackedUid;