to make it happen you can add some code to jem.css and edit the editevent-view.
one solution can be to create a template-override for the editevent view by using Joomla Template manager. By doing that the changes in the code won't be overwritten by updates.
when you did create an override then the file needed should be located over here:
Edit the page and remove this code
<li><?php echo $this->form->getLabel('locid'); ?> <?php echo $this->form->getInput('locid'); ?></li>
<li><?php echo $this->form->getLabel('contactid'); ?> <?php echo $this->form->getInput('contactid'); ?></li>
the thing is that to remove that section you need to remove the code as it can't be addressed that easily, this as it's not having a specific class.
Well, the fields are now gone but you still have the toggle editor button and the "other tab" left and to hide those the easiest would be to add some code to jem.css or use a custom css file. a custom css file can be specified in the backend of jem, tab "layout".
add this to the css file
to note: the "toggle editor" is a special one and can't be easily hidden. Other buttons can be easily disabled in the backend of joomla by going to the plugin section and tick in "button" and then turn on/off the button.