QPageSize: remove redundant operator== declaration

Amends a45a3b1ece490bcae5cccd858dbe11408a19bee0, which added the hidden
friend as an inline function, without removing the already existing
declaration. Since that declaration was exported, keep it in the ABI
via Q_REMOVED_API, and only remove it from the API.

Fixes: QTBUG-115583
Pick-to: 6.7
Change-Id: I169b565ed02168248f96c1379f537b90b4ea481c
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/gui/compat/removed_api.cpp

@@ -7,6 +7,17 @@
 
 QT_USE_NAMESPACE
 
+#if QT_GUI_REMOVED_SINCE(6, 4)
+
+#include "qpagesize.h" // removed duplicate declaration of op==
+                       // (still caused an symbol on some platforms)
+
+// #include "qotherheader.h"
+// // implement removed functions from qotherheader.h
+// order sections alphabetically
+
+#endif // QT_GUI_REMOVED_SINCE(6, 4)
+
 #if QT_GUI_REMOVED_SINCE(6, 6)
 
 #include "qpixmapcache.h" // inlined API

src/gui/painting/qpagesize.h

@@ -203,7 +203,9 @@ public:
 
     void swap(QPageSize &other) noexcept { d.swap(other.d); }
 
+#if QT_GUI_REMOVED_SINCE(6, 4)
     friend Q_GUI_EXPORT bool operator==(const QPageSize &lhs, const QPageSize &rhs);
+#endif
     bool isEquivalentTo(const QPageSize &other) const;
 
     bool isValid() const;