libstdc++: remove redundant equality operators

Now that operator<=> is supported, these operators can be generated by
the compiler.

	* include/bits/iterator_concepts.h (unreachable_sentinel_t): Remove
	redundant equality operators.
	* testsuite/util/testsuite_iterators.h (test_range::sentinel):
	Likewise.

From-SVN: r277888

libstdc++-v3/ChangeLog

+2019-11-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/iterator_concepts.h (unreachable_sentinel_t): Remove
+	redundant equality operators.
+	* testsuite/util/testsuite_iterators.h (test_range::sentinel):
+	Likewise.
+
 2019-11-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	* libsupc++/compare: New header.

libstdc++-v3/include/bits/iterator_concepts.h

@@ -797,23 +797,6 @@ namespace ranges
       friend constexpr bool
       operator==(unreachable_sentinel_t, const _It&) noexcept
       { return false; }
-
-#ifndef __cpp_lib_three_way_comparison
-    template<weakly_incrementable _It>
-      friend constexpr bool
-      operator!=(unreachable_sentinel_t, const _It&) noexcept
-      { return true; }
-
-    template<weakly_incrementable _It>
-      friend constexpr bool
-      operator==(const _It&, unreachable_sentinel_t) noexcept
-      { return false; }
-
-    template<weakly_incrementable _It>
-      friend constexpr bool
-      operator!=(const _It&, unreachable_sentinel_t) noexcept
-      { return true; }
-#endif
   };
 
   inline constexpr unreachable_sentinel_t unreachable_sentinel{};

libstdc++-v3/testsuite/util/testsuite_iterators.h

@@ -677,15 +677,6 @@ namespace __gnu_test
 
 	  friend bool operator==(const sentinel& s, const I& i)
 	  { return s.end == i.ptr; }
-
-	  friend bool operator!=(const sentinel& s, const I& i)
-	  { return !(s == i); }
-
-	  friend bool operator==(const I& i, const sentinel& s)
-	  { return s == i; }
-
-	  friend bool operator!=(const I& i, const sentinel& s)
-	  { return !(s == i); }
 	};
 
       auto