Fix not parsed message on Special:Import

Fix not parsed message on Special:Import

If session data is lost between the transactions (read: the csrf token
does not match), the error message contains some wiki markup as well as
HTML. However, unfortunately, SpecialImport uses $out->wrapWikiMsg() in
combination with an error message (with wiki markup and HTML) wrapped as
a parameter of another message. This results in an escaped paramater and
it is not parsed correctly, which leads in wiki markup send to the user.

This change fixes that issue by parsing the message directly.

Bug: T172114
Change-Id: If49a600173c44d098f25d6e2a9b87b7b7bf3ee2a