Remove nonexistant MIME type from desktop file

x-xdg-protocol has never been a way to bind to a schema in XDG.

Signed-off-by: Jerome Leclanche <jerome@leclan.ch>

lib/xdg/telegramdesktop.desktop

@@ -9,4 +9,4 @@ Terminal=false
 StartupWMClass=Telegram
 Type=Application
 Categories=Network;
-MimeType=application/x-xdg-protocol-tg;x-scheme-handler/tg;
+MimeType=x-scheme-handler/tg;