Delete unused IptcKey copy operator

include/exiv2/datasets.hpp

@@ -268,17 +268,11 @@ namespace Exiv2 {
         IptcKey(uint16_t tag, uint16_t record);
         //! Copy constructor
         IptcKey(const IptcKey& rhs);
+        IptcKey& operator=(const IptcKey& rhs) = delete;
         //! Destructor
         ~IptcKey() override = default;
         //@}
 
-        //! @name Manipulators
-        //@{
-        /*!
-          @brief Assignment operator.
-         */
-        IptcKey& operator=(const IptcKey& rhs);
-        //@}
 
         //! @name Accessors
         //@{

src/datasets.cpp

@@ -568,17 +568,6 @@ namespace Exiv2 {
     {
     }
 
-    IptcKey& IptcKey::operator=(const IptcKey& rhs)
-    {
-        if (this == &rhs)
-            return *this;
-        Key::operator=(rhs);
-        tag_ = rhs.tag_;
-        record_ = rhs.record_;
-        key_ = rhs.key_;
-        return *this;
-    }
-
     std::string IptcKey::key() const
     {
         return key_;