Add install of appdata for xdg_install_f

[ljden]

This adds the installation of appdata.xml for xdg_install_f() and corresponding remove in xdg_uninstall_f() for completeness.

Also removes unnecessary echo that is no longer required as commands no longer have sudo - see 702976f8d6f7707b275d81d26f69c8c5dd8868d1

This addresses #11806

[CLAassistant]

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