Currently there is no way on the backend (UI) for unregistering a post type, the
process however is quite simple.
Andrew Nacin provided some code over on https://core.trac.wordpress.org/ticket/14761
You can easily create a plugin with this function and have the CPT unregister.
if ( ! function_exists( 'unregister_post_type' ) ) :
function unregister_post_type( $post_type ) {
global $wp_post_types;
if ( isset( $wp_post_types[ $post_type ] ) ) {
unset( $wp_post_types[ $post_type ] );
return true;
}
return false;
}
endif;