Fix build

hphp/runtime/base/policy_array.h

@@ -342,10 +342,6 @@ public:
    */
   static bool IsVectorData(const ArrayData*);
 
-  virtual SharedVariant *getSharedVariant() const FOLLY_OVERRIDE {
-    return nullptr;
-  }
-
   /**
    * Testing whether a key exists.
    */