delete Variant::same, implement same(CVarRef, CVarRef) in terms of tvSame

Step two.  Leaving the Variant::same methods as deleted for
now because I'm worried about the implicit conversion operators to
other types that support same.

hphp/runtime/base/array/array_data.h

@@ -443,7 +443,7 @@ public:
   virtual void dump(std::ostream &os);
 
   /**
-   * Comparisons. Similar to serialize(), we implemented it here generically.
+   * Comparisons.
    */
   int compare(const ArrayData *v2) const;
   bool equal(const ArrayData *v2, bool strict) const;