Remove tests which reference an aubergine screen

A long time ago it was possible to choose your language when first booting the Ubuntu live cd and to choose an installation method like free software only. That is only still possible with Ubuntu 20.04 and that release of Ubuntu saw it's last point release in March of 2023. So any tests referencing this boot screen and the options in it should be cleaned up in the repository.

This is very low priority but its worth mentioning.

Here are some references:

 $ rg "aubergine" testcases/image/*
testcases/image/1313_Installation Broken Internet
17: <dt>Boot up the image. When you see the aubergine screen with an icon at the bottom, press any key to get the menu</dt>

testcases/image/1312_Non-English Installation No Network
16: <dt>Boot up the image. When you see the aubergine screen with an icon at the bottom, press any key to get the menu</dt>

testcases/image/1307_Free Software Only
4: <dt>Boot up the image. When you see the aubergine screen with an icon at the bottom, press any key to get the menu</dt>

testcases/image/1311_Non-English Installation Full Network Support
14: <dt>Boot up the image. When you see the aubergine screen with an icon at the bottom, press any key to get the menu</dt>

testcases/image/1316_Non-English Installation Full Network Support & CJK Input
3: <dt>Boot up the image. When you see the aubergine screen with an icon at the bottom, press any key to get the menu</dt>