Remove extra double quotes from Realm

According to Go documents `%q` already wraps string with double quotes.

    %s	the uninterpreted bytes of the string or slice
    %q	a double-quoted string safely escaped with Go syntax
    %x	base 16, lower-case, two characters per byte
    %X	base 16, upper-case, two characters per byte

This produces a header like this and breaks Perl LWP::UserAgent->credentials 

    HTTP/1.1 401 Unauthorized
    Content-Type: text/plain; charset=utf-8
    Www-Authenticate: Basic realm=""Restricted""
    Date: ...
    Content-Length: 13

Thus, I removed extra quotes and Realm value is now correctly escaped and wrapped into quotes only once[1]]

    Www-Authenticate: Basic realm="Restricted"

[0]: http://golang.org/pkg/fmt/
[1]: http://en.wikipedia.org/wiki/Basic_access_authentication#Server_side