mpkg: do_list_installed: use pkg_is_user_installed function.
mpkg: do_list_installed: use pkg_is_user_installed function.

Because this function exists!

Signed-off-by: Gaël PORTAY <1666f60cfa201a60b0ea694168a0b6932673170a@gmail.com>

gazoo74/mpkg,gazoo74/mpkg