QFontDatabase: remove outdated comments

QtBase/2526df506bda99f9497e83a4e6820557a722660e has
resolved what the comment said.

As a drive-by, remove the unused QSystemLibrary include,
which is forgotten in 2526df506b.

Amends commit 2526df506b

Pick-to: 6.3
Change-Id: Iab5c7d00e22d306be63d7588ea44bf73d377793d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/text/windows/qwindowsfontdatabase.cpp

@@ -52,7 +52,6 @@
 #include <QtCore/QFile>
 #include <QtCore/QtEndian>
 #include <QtCore/private/qduplicatetracker_p.h>
-#include <QtCore/private/qsystemlibrary_p.h>
 #include <QtCore/private/qwinregistry_p.h>
 
 #include <wchar.h>
@@ -69,10 +68,6 @@
 QT_BEGIN_NAMESPACE
 
 #if QT_CONFIG(directwrite)
-// ### fixme: Consider direct linking of dwrite.dll once Windows Vista pre SP2 is dropped (QTBUG-49711)
-
-typedef HRESULT (WINAPI *DWriteCreateFactoryType)(DWRITE_FACTORY_TYPE, const IID &, IUnknown **);
-
 static inline bool useDirectWrite(QFont::HintingPreference hintingPreference,
                                   const QString &familyName = QString(),
                                   bool isColorFont = false)

src/gui/text/windows/qwindowsfontdatabasebase.cpp

@@ -40,7 +40,6 @@
 #include "qwindowsfontdatabasebase_p.h"
 #include "qwindowsfontdatabase_p.h"
 
-#include <QtCore/private/qsystemlibrary_p.h>
 #include <QtCore/QThreadStorage>
 #include <QtCore/QtEndian>