backports: use check-lxdialog.sh

We ship it, so we should use it. This should fix issues
like one distro needing "-lncurses -ltinfo" and others
requiring just "-lncurses" and not having "tinfo".

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>