Add this following code to your themes functions.php
function custom_menu_page_removing() {
remove_menu_page('vc-general'); //vc
}
add_action( 'admin_menu', 'custom_menu_page_removing' );This is how to find out for the next time:
The link for Visual-Composer main page is admin.php?page=vc-general if you want to hide a link from an plugin in the admin backend, simply use everything behind the ?page= in this case it’s vc-general
Source: http://wordpress.stackexchange.com/questions/227593/remove-visual-composer-tab-from-dashboard-menu