[ADT] Remove STLForwardCompat.h's C++17 equivalents

[jloser]

Summary

As a follow-up of e8578968f684997840f680ed62bff5cad0accc13 which replaced the
callers to use the C++17 equivalents, remove the equivalents from
STLForwardCompat.h entirely and their corresponding tests.

llvm/include/llvm/ADT/STLForwardCompat.h

 #ifndef LLVM_ADT_STLFORWARDCOMPAT_H
 #define LLVM_ADT_STLFORWARDCOMPAT_H
 
 #include <type_traits>
 
 namespace llvm {
 
 //===----------------------------------------------------------------------===//
-//     Features from C++17
-//===----------------------------------------------------------------------===//
-
-template <typename T>
-struct negation // NOLINT(readability-identifier-naming)
-    : std::integral_constant<bool, !bool(T::value)> {};
-
-template <typename...>
-struct conjunction // NOLINT(readability-identifier-naming)
-    : std::true_type {};
-template <typename B1> struct conjunction<B1> : B1 {};
-template <typename B1, typename... Bn>
-struct conjunction<B1, Bn...>
-    : std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
-
-template <typename...>
-struct disjunction // NOLINT(readability-identifier-naming)
-    : std::false_type {};
-template <typename B1> struct disjunction<B1> : B1 {};
-template <typename B1, typename... Bn>
-struct disjunction<B1, Bn...>
-    : std::conditional<bool(B1::value), B1, disjunction<Bn...>>::type {};
-
-struct in_place_t // NOLINT(readability-identifier-naming)
-{
-  explicit in_place_t() = default;
-};
-/// \warning This must not be odr-used, as it cannot be made \c inline in C++14.
-constexpr in_place_t in_place; // NOLINT(readability-identifier-naming)
-
-template <typename T>
-struct in_place_type_t // NOLINT(readability-identifier-naming)
-{
-  explicit in_place_type_t() = default;
-};
-
-template <std::size_t I>
-struct in_place_index_t // NOLINT(readability-identifier-naming)
-{
-  explicit in_place_index_t() = default;
-};
-
-//===----------------------------------------------------------------------===//
 //     Features from C++20
 //===----------------------------------------------------------------------===//
 
 template <typename T>
 struct remove_cvref // NOLINT(readability-identifier-naming)
 {
   using type = std::remove_cv_t<std::remove_reference_t<T>>;
 };
 
 template <typename T>
 using remove_cvref_t // NOLINT(readability-identifier-naming)
     = typename llvm::remove_cvref<T>::type;
 
 } // namespace llvm
 
 #endif // LLVM_ADT_STLFORWARDCOMPAT_H

llvm/unittests/ADT/STLForwardCompatTest.cpp

 //===- STLForwardCompatTest.cpp - Unit tests for STLForwardCompat ---------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/STLForwardCompat.h"
 #include "gtest/gtest.h"
 
 namespace {
 
-TEST(STLForwardCompatTest, NegationTest) {
-  EXPECT_TRUE((llvm::negation<std::false_type>::value));
-  EXPECT_FALSE((llvm::negation<std::true_type>::value));
-}
-
-struct incomplete_type;
-
-TEST(STLForwardCompatTest, ConjunctionTest) {
-  EXPECT_TRUE((llvm::conjunction<>::value));
-  EXPECT_FALSE((llvm::conjunction<std::false_type>::value));
-  EXPECT_TRUE((llvm::conjunction<std::true_type>::value));
-  EXPECT_FALSE((llvm::conjunction<std::false_type, incomplete_type>::value));
-  EXPECT_FALSE((llvm::conjunction<std::false_type, std::true_type>::value));
-  EXPECT_FALSE((llvm::conjunction<std::true_type, std::false_type>::value));
-  EXPECT_TRUE((llvm::conjunction<std::true_type, std::true_type>::value));
-  EXPECT_TRUE((llvm::conjunction<std::true_type, std::true_type,
-                                 std::true_type>::value));
-}
-
-TEST(STLForwardCompatTest, DisjunctionTest) {
-  EXPECT_FALSE((llvm::disjunction<>::value));
-  EXPECT_FALSE((llvm::disjunction<std::false_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::true_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::true_type, incomplete_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::false_type, std::true_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::true_type, std::false_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::true_type, std::true_type>::value));
-  EXPECT_TRUE((llvm::disjunction<std::true_type, std::true_type,
-                                 std::true_type>::value));
-}
-
 template <typename T>
 class STLForwardCompatRemoveCVRefTest : public ::testing::Test {};
 
 using STLForwardCompatRemoveCVRefTestTypes = ::testing::Types<
     // clang-format off
     std::pair<int, int>,
     std::pair<int &, int>,
     std::pair<const int, int>,