Bug#866086: Remove warning on no selecting swap partition

[Narcis Garcia <debianlists@actiu.net>]

Package: debian-installer
Version: 20170615
Severity: important
Tags: d-i

"You have not selected any partitions for use as swap space..."
And default option is to return to the partitioning menu.

This is very confusing to unexperienced users and nonsense with
computers with lots of RAM.

I've tested an scenario with 16GiB of "hard disk" and 16GiB of RAM:
debian-installer (partition tool:manual) complains about not creating a
swap partition.
Additionally, when using "Guided partitioning" option (single), it
creates a system partition of 3.7GiB and swap partition of 12.3GiB