The mpm event module in Ubuntu 13.10 uses the following files, which are removed: -

Notice: /Stage[main]/Apache/File[/etc/apache2/mods-available/mpm_event.load]/ensure: removed
Notice: /Stage[main]/Apache/File[/etc/apache2/mods-enabled/mpm_event.load]/ensure: removed
Notice: /Stage[main]/Apache/File[/etc/apache2/mods-available/mpm_event.conf]/ensure: removed
Notice: /Stage[main]/Apache/File[/etc/apache2/mods-enabled/mpm_event.conf]/ensure: removed

This file creates an event.conf file.

Taking these lines back out of this file gives the following error whilst trying to restart apache2 on Ubuntu 13.10: -

   Output of config test was:
   AH00534: apache2: Configuration error: No MPM loaded.
   Action 'configtest' failed.

Up until Ubuntu 13.10 the mpm was built into the apache2 binary, hence apache2-mpm-prefork, etc.
Now, on Ubuntu 13.10 its a separate module needing the separate LoadModule