In `WP_Widget::update_callback()`, `$sidebars_widgets` is unused.

See #27882.


git-svn-id: https://develop.svn.wordpress.org/trunk@28338 602fd350-edb4-49c9-b593-d223f7449a82
In `wpdb`, remove dead code:

* In `->tables()`, `break` is unreachable after `return`
* In `->query()`, `$return` is always set, so doesn't need an initial value of `0`
* In `->delete()`, `$bits` is unused

See #27882.


git-svn-id: https://develop.svn.wordpress.org/trunk@28339 602fd350-edb4-49c9-b593-d223f7449a82
In `wp-login.php`, `break` is unreachable after `exit`

See #27882.


git-svn-id: https://develop.svn.wordpress.org/trunk@28340 602fd350-edb4-49c9-b593-d223f7449a82