while cleaning up a long-running Joomla site (migrated over the years from Joomla 2.5 all the way to 5.4, with Admin Tools installed and kept up to date throughout), I found a leftover from what I believe is a very old Admin Tools release: the discontinued "Akeeba Version Check" system plugin (plg_system_akversioncheck).
The situation on my site was as follows:
The plugin folder plugins/system/akversioncheck/ still existed, containing the legacy (pre-namespace) plugin code.
The plugin was still registered and enabled in #__extensions, so it was being loaded on every request.
Its package_id still pointed to the current pkg_admintools package. Because of that, Joomla refused to uninstall it individually with the message that it is part of a package that does not allow uninstalling individual extensions. Uninstalling the package itself was obviously not an option, as that would have removed the current Admin Tools installation.
Workaround that solved it cleanly: UPDATE #__extensions SET package_id = 0 WHERE extension_id = ; — after that, a regular uninstall through the Extensions Manager worked and removed both the database entry and the folder.
Two related leftovers I also found in administrator/language/en-GB/, apparently from old Admin Tools versions: en-GB.plg_installer_admintools.ini / .sys.ini (no matching plugin folder exists under plugins/installer/ anymore) and en-GB.com_admintools.menu.ini.
Request: Could you consider adding a cleanup step to the Admin Tools package install/update script that removes the obsolete akversioncheck plugin (files and #__extensions row, or at least detaches it from pkg_admintools so users can uninstall it themselves), and deletes the orphaned language files listed above? Sites that have been upgraded across major Joomla versions for a decade are likely to carry these same leftovers without knowing it.
Thank you for your work on Admin Tools!