Remove the no longer used is_unique type trait

It was used in checking that types in TEMPLATE_TEST_CASE and friends
were unique, but this was removed for v2.8.0 (#1628). Since there
are no further uses of this trait, the simplest thing to do is to
just remove it.

Fixes #1757

include/internal/catch_test_registry.h

@@ -12,7 +12,6 @@
 #include "catch_interfaces_testcase.h"
 #include "catch_compiler_capabilities.h"
 #include "catch_stringref.h"
-#include "catch_type_traits.hpp"
 #include "catch_preprocessor.hpp"
 #include "catch_meta.hpp"
 

include/internal/catch_type_traits.hpp

@@ -1,40 +0,0 @@
-/*
- *  Created by Jozef on 12/11/2018.
- *  Copyright 2017 Two Blue Cubes Ltd. All rights reserved.
- *
- *  Distributed under the Boost Software License, Version 1.0. (See accompanying
- *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- */
-
-#ifndef TWOBLUECUBES_CATCH_TYPE_TRAITS_HPP_INCLUDED
-#define TWOBLUECUBES_CATCH_TYPE_TRAITS_HPP_INCLUDED
-
-#include <type_traits>
-
-namespace Catch{
-
-#ifdef CATCH_CPP17_OR_GREATER
-	template <typename...>
-	inline constexpr auto is_unique = std::true_type{};
-
-	template <typename T, typename... Rest>
-	inline constexpr auto is_unique<T, Rest...> = std::bool_constant<
-		(!std::is_same_v<T, Rest> && ...) && is_unique<Rest...>
-	>{};
-#else
-
-template <typename...>
-struct is_unique : std::true_type{};
-
-template <typename T0, typename T1, typename... Rest>
-struct is_unique<T0, T1, Rest...> : std::integral_constant
-<bool,
-     !std::is_same<T0, T1>::value 
-     && is_unique<T0, Rest...>::value 
-     && is_unique<T1, Rest...>::value
->{};
-
-#endif
-}
-
-#endif // TWOBLUECUBES_CATCH_TYPE_TRAITS_HPP_INCLUDED