Moodle 3.9+ (Build: 20200626) -Activity Chooser Hangs because of orphaned plugin

cf. https://moodle.org/mod/forum/discuss.php?d=406137

In an install of build 20200626 with an orphan plugin, activity chooser hangs and never loads and turning off "Site Administration > Appearance > AJAX and Javascript > Activity chooser default" causes course pages or site home to stop rendering when editing is turned on with the error message "Coding error detected, it must be fixed by a programmer: Invalid component used in plugin/component_callback():assignment_onlineaudio" (with the last being the orphaned plugin).

New activities cannot be created on the affected sites through the Web interface.

Moodle 3.9+ build 20200626
Mariadb 10.3.23
php 7.2.24.0.0.18.04.6

Ubuntu 18.04 LTS