duplicate login message on raspberry pi core18 image

[Ian Johnson]

On a fresh UC18 image from http://cdimage.ubuntu.com/ubuntu-core/18/stable/current/ubuntu-core-18-armhf+raspi3.img.xz on a Raspberry Pi 3B+, I see the following upon logging in over SSH:

```
$ ssh ubuntu@$IP_ADDRESS
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-1041-raspi2 armv7l)
This system has been minimized by removing packages and content that are
not required on a system that users do not log into.

To restore this content, you can run the 'unminimize' command.
 * Ubuntu Core: https://www.ubuntu.com/core
 * Community: https://forum.snapcraft.io
 * Snaps: https://snapcraft.io

This Ubuntu Core 18 machine is a tiny, transactional edition of Ubuntu,
designed for appliances, firmware and fixed-function VMs.

If all the software you care about is available as snaps, you are in
the right place. If not, you will be more comfortable with classic
deb-based Ubuntu Server or Desktop, where you can mix snaps with
traditional debs. It's a brave new world here in Ubuntu Core!

Please see 'snap --help' for app installation and updates.
ubuntu@localhost:~$
```

The first few lines:

```
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-1041-raspi2 armv7l)
This system has been minimized by removing packages and content that are
not required on a system that users do not log into.

To restore this content, you can run the 'unminimize' command.
```

seems erroneous on a core image. This is also a bug because one can't run the "unminimize" command to "restore" the non-minimal aspects of the image.

[Zygmunt Krynicki (zyga)]

I saw this numerous times and it was reported to me at several events. Marking as confirmed.

[Łukasz Zemczak (sil2100)]

PR is up for review.

[Zygmunt Krynicki (zyga)]

Łukasz, can you please provide the pull request number as a comment. This tremendously simplifies bug gardening.