Switching to wporg-developer theme causes PHP warning

[DJPaul]

When switching *to* the wporg-developer theme, a PHP warning occurs:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'DevHub\add_roles' not found or invalid function name in /srv/www/wordpress-develop/src/wp-includes/plugin.php on line

Patch attached which corrects the path to the function of that same name (I'm assuming that's what the original author intended, to set up the new role when the theme is activated).

[coffee2code]

In 1821:

developer.wordpress.org: Handbook-related hooking changes that should have been included in r953.

• Move hooking of 'after_switch_theme' from functions.php to inc/handbooks.php. Fixes warning since the hooked function was previously moved over.
• Remove hooking 'wporg_action_links' in functions.php since that had already been moved over.

Props DJPaul.
Fixes #1177.