QFuture/QPromise: don't check for is_copy_constructible

The check is over-arching. is_move_constructible is sufficient;
we don't have to support "ridiculous" types that are copiable but
have deleted move operations (such types are fundamentally broken).
This is in line with the Move* (legacy) named requirements.

Change-Id: Idc7116b39013501b9be39628a4e7afd35fe15530
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>

src/corelib/thread/qfuture.h

@@ -59,10 +59,9 @@ class QFutureWatcher;
 template <typename T>
 class QFuture
 {
-    static_assert (std::is_copy_constructible_v<T>
-                   || std::is_move_constructible_v<T>
+    static_assert (std::is_move_constructible_v<T>
                    || std::is_same_v<T, void>,
-                   "Type with copy or move constructors or type void is required");
+                   "A move-constructible type or type void is required");
 public:
     QFuture()
         : d(QFutureInterface<T>::canceledResult())

src/corelib/thread/qpromise.h

@@ -52,10 +52,9 @@ QT_BEGIN_NAMESPACE
 template<typename T>
 class QPromise
 {
-    static_assert (std::is_copy_constructible_v<T>
-                   || std::is_move_constructible_v<T>
+    static_assert (std::is_move_constructible_v<T>
                    || std::is_same_v<T, void>,
-                   "Type with copy or move constructors or type void is required");
+                   "A move-constructible type or type void is required");
 public:
     QPromise() = default;
     Q_DISABLE_COPY(QPromise)

tests/auto/corelib/thread/qpromise/tst_qpromise.cpp

@@ -77,7 +77,6 @@ private slots:
 
 struct TrivialType { int field = 0; };
 struct CopyOnlyType {
-    Q_DISABLE_MOVE(CopyOnlyType)
     constexpr CopyOnlyType(int field = 0) noexcept : field(field) {}
     CopyOnlyType(const CopyOnlyType &) = default;
     CopyOnlyType& operator=(const CopyOnlyType &) = default;