Comment 6 for bug 1828100

I went ahead and disabled the identifyObsoleteKernels function and here is the relevant part of /var/log/dist-upgrade/main.log:

2019-06-19 15:37:29,707 DEBUG Obsolete: libisl19 libpoppler85 linux-headers-5.0.0-13 linux-headers-5.0.0-13-generic linux-image-5.0.0-13-generic linux-modules-5.0.0-13-generic linux-modules-extra-5.0.0-13-generic
2019-06-19 15:37:29,707 DEBUG Foreign:
2019-06-19 15:37:29,707 DEBUG forced_obsoletes: ['desktop-effects', 'gnome-app-install', 'policykit-gnome', 'gnome-mount']
2019-06-19 15:37:30,001 DEBUG Unused dependencies: libisl19 pppconfig ifupdown libpoppler85 pppoeconf
2019-06-19 15:37:30,001 DEBUG remove_candidates: '{'libisl19', 'linux-image-5.0.0-13-generic', 'gnome-mount', 'policykit-gnome', 'desktop-effects', 'linux-modules-5.0.0-13-generic', 'pppconfig', 'linux-modules-extra-5.0.0-13-generic', 'gnome-app-install', 'libpoppler85', 'ifupdown', 'linux-headers-5.0.0-13', 'linux-headers-5.0.0-13-generic', 'pppoeconf'}'
2019-06-19 15:37:30,001 DEBUG Start checking for obsolete pkgs
2019-06-19 15:37:30,100 DEBUG skipping running kernel pkg 'linux-image-5.0.0-13-generic'
2019-06-19 15:37:30,100 DEBUG 'linux-image-5.0.0-13-generic' scheduled for remove but not safe to remove, skipping
2019-06-19 15:37:30,101 DEBUG skipping running kernel pkg 'linux-modules-5.0.0-13-generic'
2019-06-19 15:37:30,101 DEBUG 'linux-modules-5.0.0-13-generic' scheduled for remove but not safe to remove, skipping
2019-06-19 15:37:30,198 DEBUG skipping running kernel pkg 'linux-modules-extra-5.0.0-13-generic'
2019-06-19 15:37:30,198 DEBUG 'linux-modules-extra-5.0.0-13-generic' scheduled for remove but not safe to remove, skipping
2019-06-19 15:37:30,720 DEBUG skipping running kernel pkg 'linux-headers-5.0.0-13-generic'
2019-06-19 15:37:30,721 DEBUG 'linux-headers-5.0.0-13-generic' scheduled for remove but not safe to remove, skipping
2019-06-19 15:37:30,822 DEBUG Finish checking for obsolete pkgs
2019-06-19 15:37:30,861 DEBUG The following packages are marked for removal: linux-headers-5.0.0-13 ifupdown linux-headers-5.0.0-13-generic pppoeconf libisl19 pppconfig libpoppler85

So just removing the function seems like the best way forward.