For Elementor Page Builder Plugin: Remove the regular WordPress Widgets from the left-hand Panel in the Live Editor. --- CAUTION: Use at your own risk! No support here!!!

elementor-remove-wp-widgets.php

<?php
/** Do NOT include the opening php tag */


if ( ! function_exists( 'ddw_tweak_elementor_remove_wp_widgets' ) ) :

	add_filter( 'elementor/widgets/black_list', 'ddw_tweak_elementor_remove_wp_widgets' );
	/**
	 * Optionally remove all WordPress widgets from the Elementor Live Editor.
	 *   Note: A native Elementor filter is used.
	 *
	 * @link https://gist.github.com/deckerweb/11878962da6f4e31877520e199254cef
	 * @author David Decker - DECKERWEB
	 *
	 * @global array $GLOBALS[ 'wp_widget_factory' ]
	 *
	 * @param array $black_list Array holding all blacklisted WordPress widgets.
	 * @return array Tweaked array of black listed WordPress widgets.
	 */
	function ddw_tweak_elementor_remove_wp_widgets( $black_list ) {

		/** Bail early if Elementor not active or tweak not wanted */
		if ( ! defined( 'ELEMENTOR_VERSION' ) ) {
			return $black_list;
		}

		/**
		 * Get all registered WordPress widgets, but only the classes
		 *   (= the first-level array keys)
		 */
		$black_list = array_keys( $GLOBALS[ 'wp_widget_factory' ]->widgets );

		/** Return black list array for filter */
		return (array) $black_list;

	}  // end function

endif;

I did it, sorry:

add_action('elementor/widgets/widgets_registered', function( $widget_manager ){
	// FREE
	$widget_manager->unregister_widget_type('read-more');
	$widget_manager->unregister_widget_type('sidebar');
	$widget_manager->unregister_widget_type('audio');
	
	// PRO
	$widget_manager->unregister_widget_type('form');
	$widget_manager->unregister_widget_type('nav-menu');

}, 15);