Utils: Remove Utils::optional

Since we are now requiring macOS 10.14 we can remove our local
implementation of optional and use std::optional for macOS too.

Change-Id: I2bd018261b68da64f7f031a812045dd7784697e1
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangtools/clangtoolsutils.h

@@ -6,10 +6,11 @@
 #include <cppeditor/clangdiagnosticconfig.h>
 
 #include <utils/id.h>
-#include <utils/optional.h>
 
 #include <QtGlobal>
 
+#include <optional>
+
 namespace CppEditor { class ClangDiagnosticConfigsModel; }
 namespace Debugger { class DiagnosticLocation; }
 namespace Utils { class FilePath; }
@@ -31,10 +32,9 @@ enum class FixitStatus {
     Invalidated,
 };
 
-QString createDiagnosticToolTipString(
-    const Diagnostic &diagnostic,
-    Utils::optional<FixitStatus> status = Utils::nullopt,
-    bool showSteps = true);
+QString createDiagnosticToolTipString(const Diagnostic &diagnostic,
+                                      std::optional<FixitStatus> status = std::nullopt,
+                                      bool showSteps = true);
 
 CppEditor::ClangDiagnosticConfig builtinConfig();