Removed useless operator<< for TNL::String

The implementation for std::string (which is a base class of
TNL::String) is perfectly sufficient.

src/TNL/String.h

@@ -21,8 +21,6 @@
 
 namespace TNL {
 
-class String;
-
 /**
  * \brief Class for managing strings.
  *
@@ -39,8 +37,6 @@ class String;
  * 
  * \ref operator+
  * 
- * \ref operator<<
- * 
  * \ref mpiSend
  * 
  * \ref mpiReceive
@@ -368,11 +364,6 @@ String operator+( const char* string1, const String& string2 );
  */
 String operator+( const std::string& string1, const String& string2 );
 
-/**
- * \brief Writes the string \e str to given \e stream
- */
-std::ostream& operator<<( std::ostream& stream, const String& str );
-
 /**
  * \brief Converts \e value of type \e T to a String.
  * 

src/TNL/String.hpp

@@ -243,12 +243,6 @@ inline String operator+( const std::string& string1, const String& string2 )
    return String( string1 ) + string2;
 }
 
-inline std::ostream& operator<<( std::ostream& stream, const String& str )
-{
-   stream << str.getString();
-   return stream;
-}
-
 #ifdef HAVE_MPI
 inline void mpiSend( const String& str, int target, int tag, MPI_Comm mpi_comm )
 {