While the Subpanel listviews are quite customizable via Studio, the one item that isn’t for the Calls, Meetings, and Tasks in the Activities subpanel is the button you can click to close an item. If you want to remove this icon, use this tip from prolific forums poster andopes:
You have to create extended layoutdefs for Leads (custom/Extension/modules/Leads/Ext/Layoutdefs/somescript.php) in order to redefine the subpanel_name for each Activities module.
Obviously you can create the folders and file if they don´t exist. Add into script a code like that:
$layout_defs['Leads']['subpanel_setup']['activities']['collection_list']['calls']['override_subpanel_name'] = 'some_script';
Duplicate the code for each module inside collection_list under activities.
Copy the script modules/Calls/metadata/subpanels/ForActivities.php into custom/modules/Calls/metadata/subpanels/some_script.php and remove the close_button from metadata.
Go to Admin -> Repair -> Quick Repair and Rebuild