Remove unused/misleading variable in wpmu_signup_blog_notification()

[iamfriendly]

The $message variable in wpmu_signup_blog_notification() contains an unused $key variable that is now part of the $activate_url var. It's been removed from the string in the sprintf call but not from the variables passed to it.
The attached patch removes the unnecessary and unused variable.

[iamfriendly]

Remove unused variable in wpmu_signup_blog_notification()

[jeremyfelt]

The addition of this $key variable dates back to changeset ​MU1977 due to the reasoning in ticket ​MU1119

It's interesting the ticket mentions adding $key to the filter, though it's really adding it to be used in sprintf().

It is possible that somebody is using the wpmu_signup_blog_notification_email filter to alter the original message to account for that 3rd variable. Because of this, I don't think that we can remove it.

[iamfriendly]

But the $key variable isn't actually passed to the sprintf call. There's only two placeholders and the $key variable is a third. Which isn't actually available in the string. Unless I'm mis-reading it, Jeremy?

[jeremyfelt]

The default message only uses %s twice, but if I were to use the filter to change that to something else that does have three placeholders - like "Hi, activate at %s, then login at %s, by the way your key is %s" - it would pick it up.

[iamfriendly]

Of course! I'm an idiot. I should not try and think this stuff through when I'm hungover ;)