Revert [23307] so new users in multisite are not automatically subscribers on the main site.

Merges [25183] to the 3.6 branch.

props duck_.
fixes #25166.
see #15627.



git-svn-id: https://develop.svn.wordpress.org/branches/3.6@25184 602fd350-edb4-49c9-b593-d223f7449a82