clang-tidy: remove const char operator

It morphs into std::string anyway.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

include/exiv2/xmp_exiv2.hpp

@@ -58,11 +58,6 @@ class EXIV2API Xmpdatum : public Metadatum {
            Calls setValue(const std::string&).
    */
   Xmpdatum& operator=(const std::string& value);
-  /*!
-    @brief Assign const char* \em value to the %Xmpdatum.
-           Calls operator=(const std::string&).
-   */
-  Xmpdatum& operator=(const char* value);
   /*!
     @brief Assign a boolean \em value to the %Xmpdatum.
            Translates the value to a string "true" or "false".
@@ -404,10 +399,6 @@ class EXIV2API XmpParser {
 // *****************************************************************************
 // free functions, template and inline definitions
 
-inline Xmpdatum& Xmpdatum::operator=(const char* value) {
-  return Xmpdatum::operator=(std::string(value));
-}
-
 inline Xmpdatum& Xmpdatum::operator=(const bool& value) {
   return operator=(value ? "True" : "False");
 }