Add `Update URI:` to `plugin.php` header metadata

[Herm71]

Update URI

WordPress 5.8 introduced Update URI: in the plugin header.

Per the WordPress Dev note:

This allows third-party plugins to avoid accidentally being overwritten with an update of a plugin of a similar name from the WordPress.org Plugin Directory.

Add any url here to prevent the plugin from accidentally being overwritten from WordPress.org.

• e.g., * Update URI: https://ucsc.edu

And we can remove the following function from plugin.php:

if ( ! function_exists( 'ucsc_custom_functionality_hidden' ) ) {
	/**
	* Don't Update Plugin
	*
	* @since 1.0.0
	*
	* This prevents you being prompted to update if there's a public plugin
	* with the same name.
	*
	* @author Mark Jaquith
	* @link http://markjaquith.wordpress.com/2009/12/14/excluding-your-plugin-or-theme-from-update-checks/
	*
	* @param array  $r, request arguments
	* @param string $url, request url
	* @return array request arguments
	*/

	function ucsc_custom_functionality_hidden( $r, $url ) {
		if ( 0 !== strpos( $url, 'http://api.wordpress.org/plugins/update-check' ) ) {
			return $r; // Not a plugin update request. Bail immediately.
		}
		$plugins = unserialize( $r['body']['plugins'] );
		unset( $plugins->plugins[ plugin_basename( __FILE__ ) ] );
		unset( $plugins->active[ array_search( plugin_basename( __FILE__ ), $plugins->active ) ] );
		$r['body']['plugins'] = serialize( $plugins );
		return $r;
	}
}

add_filter( 'http_request_args', 'ucsc_custom_functionality_hidden', 5, 2 );