Remove WordPress emojis without a plugin.

functions.php

<?php

/* @link https://anythinggraphic.net/disable-emojis-in-wordpress-without-a-plugin
/* Remove emoji scripts and dns prefetch
----------------------------------------------------------------------------------------*/
add_action( 'init', 'ag_disable_wp_emojicons' );
function ag_disable_wp_emojicons() {
	// all actions related to emojis
	remove_action( 'admin_print_styles', 'print_emoji_styles' );
	remove_action( 'wp_head', 'print_emoji_detection_script', 7 );
	remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
	remove_action( 'wp_print_styles', 'print_emoji_styles' );
	remove_filter( 'wp_mail', 'wp_staticize_emoji_for_email' );
	remove_filter( 'the_content_feed', 'wp_staticize_emoji' );
	remove_filter( 'comment_text_rss', 'wp_staticize_emoji' );

	// filter to remove TinyMCE emojis, below
	add_filter( 'tiny_mce_plugins', 'ag_disable_emojicons_tinymce' );
}
function ag_disable_emojicons_tinymce( $plugins ) {
	if ( is_array( $plugins ) ) {
		return array_diff( $plugins, array( 'wpemoji' ) );
			} else {
		return array();
	}
}
// Lastly, remove the DNS Prefetch
add_filter( 'emoji_svg_url', '__return_false' );