QModelIndex: remove user-defined copy operations

They're identical to the ones the compiler will
synthesize and their presence prevents move
constructor and assignment operators from being
synthesized alongside their copy counterparts.

The destructor can go, too.

Change-Id: Ia9cc26ba1ffaa670f03642af457e632f44bd69c2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/itemmodels/qabstractitemmodel.h

@@ -61,9 +61,7 @@ class Q_CORE_EXPORT QModelIndex
     friend class QProxyModel;
 public:
     inline QModelIndex() : r(-1), c(-1), p(0), m(0) {}
-    inline QModelIndex(const QModelIndex &other)
-        : r(other.r), c(other.c), p(other.p), m(other.m) {}
-    inline ~QModelIndex() { p = 0; m = 0; }
+    // compiler-generated copy/move ctors/assignment operators are fine!
     inline int row() const { return r; }
     inline int column() const { return c; }
     inline void *internalPointer() const { return p; }