gdate: Drop unnecessary use of G_DISABLE_DEPRECATED
gdate: Drop unnecessary use of G_DISABLE_DEPRECATED

The function is already annotated with `GLIB_DEPRECATED_FOR()`.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib