I would try the following:
- to find out what is installed
aptitude search '~iapache'
- why it is installed
aptitude why apache2-mpm-worker
maybe this one is only recommended by another package
- and what depends on this package
aptitude search '~i~Dapache2-mpm-worker'
- finally, see what would happen, if it is removed:
aptitude -s purge apache2-mpm-worker
--
Best regards,
Jörg-Volker.