A non instrusive way to achive this is through a custom app.
In a custom app in hooks.py configure the app_include_js variable with something like:
app_include_js = "/assets/yourapp/js/hide_help_menu.js"
Under /yourapp/public/ folder create the hide_help_menu.js file with
$(function() {
$('.dropdown-help').hide(); // or .remove();
});