meson build: drop desktop-file argument
meson build: drop desktop-file argument

- fixes building with meson-0.62.0

With meson-0.62.0 this deprecation warning will cause an error.
`DEPRECATION: i18n.merge_file does not take any positional arguments.
 This will become a hard error in the next Meson release.`

mate-desktop/mozo,mate-desktop/mozo