Make the script load in the User namespace, remove User_talk

`wgPageName.indexOf('User:*')` typo(?) converted to
`wgPageName.indexOf('User:')`. Additionally, remove User_talk from
core.js, since *it will never evaluate to true* because core.js is
*never* loaded in the User_talk namespace. @wikipedia-mabdul, this all
okay? or was there a reason for the star in there?