libstdc++: Fix redundant assignment (PR 94629)

This appears to be a copy&paste error, which cppcheck diagnoses.

	PR other/94629
	* include/debug/formatter.h (_Error_formatter::_Parameter): Fix
	redundant assignment in constructor.

libstdc++-v3/ChangeLog

+2020-04-19  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR other/94629
+	* include/debug/formatter.h (_Error_formatter::_Parameter): Fix
+	redundant assignment in constructor.
+
 2020-04-18  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/chrono (duration, time_point): Define operator<=> and

libstdc++-v3/include/debug/formatter.h

@@ -300,7 +300,6 @@ namespace __gnu_debug
 	  _M_variant._M_iterator._M_address = std::__addressof(__it);
 	  _M_variant._M_iterator._M_type = _GLIBCXX_TYPEID(_Iterator);
 	  _M_variant._M_iterator._M_constness =
-	  _M_variant._M_iterator._M_constness =
 	    __it._S_constant() ? __const_iterator : __mutable_iterator;
 	  _M_variant._M_iterator._M_sequence = __it._M_get_sequence();
 	  _M_variant._M_iterator._M_seq_type = _GLIBCXX_TYPEID(_Sequence);