How hide “ALL” menu item for users?
The menu is being created in the file themes/<THEME_NAME>/tpls/_headerModuleList.tpl
you can check the foreach loops and Last condition where it populates all modules.
In order to make an upgrade safe change to the theme TPL file copy so that the path becomes
custom/themes/<THEME_NAME>/tpls/_headerModuleList.tpl
The following worked for me:
In: /include/MVC/View
Comment/Remove this line (it is present twice):
$groupTabs[$app_strings[‘LBL_TABGROUP_ALL’]][‘modules’] = $fullModuleList;
I hope it helps 
IMPORTANT UPDATE: this will also break the menu links when the window is resized or in a mobile device