Clean up duplicate hook notations and adjacency for calls to the `wp_signup_location` filter.

Also adds braces missed in [25535].

See #26869.

Built from https://develop.svn.wordpress.org/trunk@28215


git-svn-id: http://core.svn.wordpress.org/trunk@28045 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Mark the `$hook` and `$page_hook` hooks as `@internal` to skip parsing.

See #26869.

Built from https://develop.svn.wordpress.org/trunk@28216


git-svn-id: http://core.svn.wordpress.org/trunk@28046 1a063a9b-81f0-0310-95a4-ce76da25c4cd