<?php

add_filter( 'mce_buttons_2', 'acme_remove_from_kitchen_sink');
/**
 * Removes the all but the formatting button from the post editor.
 *
 * @since    1.0.0
 *
 * @param    array    $buttons    The current array buttons including the kitchen sink.
 * @return   array                The updated array of buttons that exludes the kitchen sink.
 */
function acme_remove_from_kitchen_sink( $buttons ) {

 	$invalid_buttons = array(
			'underline',
			'justifyfull',
			'forecolor',
			'|',
			'pastetext',
			'pasteword',
			'removeformat',
			'charmap',
			'outdent',
			'indent',
			'undo',
			'redo',
			'wp_help'
		);


	
	foreach ( $buttons as $button_key => $button_value ) {
    
    		if ( in_array( $button_value, $invalid_buttons ) ) {
      			unset( $buttons[ $button_key ] );
    		}
    
	}

	return $buttons;

}

https://gist.github.com/tommcfarlin/86e4f040bcc641a86f59

Thanks to Tom McFarlin for this: https://gist.github.com/tommcfarlin/86e4f040bcc641a86f59

WordPress Remove buttons from the TinyMCE editor

wordpress

PHP