SECURITY: Don't parse usernames as wikitext

On Special:PasswordReset, don't parse the username as wikitext since
the wikitext is parsed according to the wiki's configuration (might
include wgRawHtml), and the wiki may be private.

Bug: 65501
Change-Id: Ic3e5d42e1be5acc42ba89ae853c5ecbfec04fa91