WordPress snippet which prevents your plugin from being included in the list of plugins sent to WordPress.org to check for updates.

plugin-file.php

<?php
/**
 * Don't update this plugin
 *
 * This prevents you from being prompted to update if there's a public plugin
 * with the same name.
 *
 * @author Phil Wylie
 * @link http://link.from.pw/1cFfcFZ
 * @param array $r Request arguments
 * @param string $url Request url
 * @return array Request arguments
 */
function pw_hidden_plugin( $r, $url ) {
	if ( 0 === strpos( $url, 'https://api.wordpress.org/plugins/update-check/1.1/' ) ) {
		$plugins = json_decode( $r['body']['plugins'], true );
		unset( $plugins['plugins'][plugin_basename( __FILE__ )] );
		$r['body']['plugins'] = json_encode( $plugins );
	}
	return $r;
}
add_filter( 'http_request_args', 'pw_hidden_plugin', 5, 2 );