Do not send a welcome notification when noconfirmation has been flagged

When adding a new user to a site on the network, 2 emails are sent out - one for confirmation and one as a welcome. If the option for no confirmation is selected, neither should send.

props transom
Fixes #16235


git-svn-id: https://develop.svn.wordpress.org/trunk@29880 602fd350-edb4-49c9-b593-d223f7449a82