netinstaller gone starting on groovy

Starting on groovy the mini.iso (netinstaller) is removed from upstream,

http://archive.ubuntu.com/ubuntu/dists/groovy/main/installer-amd64/current/legacy-images/

Changelong,

debian-installer (20101020ubuntu622.2) groovy; urgency=medium

  * Stop building legacy-images. LP: #1884538

 -- Dimitri John Ledkov <xnox@ubuntu.com>  Mon, 22 Jun 2020 14:50:43 +0100

debian-installer (20101020ubuntu621) groovy; urgency=medium

  * Correctly quote UDEB_COMPONENTS.

 -- Dimitri John Ledkov <xnox@ubuntu.com>  Thu, 28 May 2020 03:20:23 +0100
...

As mentioned in LP:#1884538

> Is it possible to keep this package in universe because community wants to build netboot image their own. That means 
keeping all the dependencies as well. But they can just sync from debian.


Not really, no. Ubuntu d-i has significant improvements over the debian one, and it would be a regression reverting to 
debian version of udebs.


Also, d-i from universe does not really work, as it has to be always be build with a matching kernel ABI _and_ all of the 
userspace abi changes, _at the same time_, implying hard interlock on our kernel release cadence. As in, one has to rebuild 
d-i with every kernel upload and ensure they migrate in sync with any in-progress ABI changes in the release. It significantly 
hinders and deadlocks distribution development. Whenver things are missmatched, d-i simply fails to fetch/download/install 
udebs and fails with critical errors saying that either kernel modules are not available or it cannot install partman udebs 
rendering it useless.