How to remove admin menu pages inserted by plugins and themes in the top admin bar?

You can play around the WP_Admin_Bar class

add_action( 'admin_bar_menu', 'modify_admin_bar' );

function modify_admin_bar( $wp_admin_bar ){
 // do something with $wp_admin_bar;
 $wp_admin_bar->get_nodes();

}

Have look to the codex WP_Admin_Bar to see all methods available.