Revert "Use gtk clipboard when available to avoid https://bugreports.qt.io/browse/QTBUG-56595"

Fixed in Qt by https://codereview.qt-project.org/c/qt/qtbase/+/306771

This reverts commit 3a91003eea.

Telegram/SourceFiles/platform/linux/linux_gtk_integration.h

@@ -25,8 +25,6 @@ public:
 
 	[[nodiscard]] bool showOpenWithDialog(const QString &filepath) const;
 
-	[[nodiscard]] QImage getImageFromClipboard() const;
-
 	static QString AllowedBackends();
 
 	static int Exec(