Remove SiteUrl from SiteSettings

This is used used and not needed with the multi-tenancy work
recently done.

--HG--
branch : dev

src/Orchard/Settings/ISite.cs

@@ -8,7 +8,6 @@ namespace Orchard.Settings {
         string PageTitleSeparator { get; }
         string SiteName { get; }
         string SiteSalt { get; }
-        string SiteUrl { get; }
         string SuperUser { get; }
         string HomePage { get; set; }
     }