Fixed Gentoo QA Notice in desktop file

 * QA Notice: This package installs one or more .desktop files that do not
 * pass validation.
 *
 *      /usr/share/applications/remmina.desktop: warning: key "OnlyShowIn" in group "Desktop Action Profile" is deprecated
 *      /usr/share/applications/remmina.desktop: warning: key "OnlyShowIn" in group "Desktop Action Tray" is deprecated
 *