set url used in createaccount-text to main page canonical url

$wgScript (index.php) appended to the site url
(e.g. https://en.wikipedia.org/w/index.php) seems pointless
in the context of these email messages.

Change-Id: I1ae1ef164aa2db66e9370640e1e7dbddbed811c2
Merge "set url used in createaccount-text to main page canonical url"