_s: Update function return values.

Adds missing documentation for `_s_categorized_blog()` and removes void
statements, in accordance with WordPress documentation guidelines.

See
http://make.wordpress.org/core/handbook/inline-documentation-standards/p
hp-documentation-standards/#phpdoc-tags

inc/wpcom.php

@@ -11,7 +11,6 @@
  * Adds support for wp.com-specific theme functions.
  *
  * @global array $themecolors
- * @return void
  */
 function _s_wpcom_setup() {
 	global $themecolors;