ParsedURL: Remove url field

This prevents a 'url' field that is out of sync with the other
fields. You can use to_string() to get the full URL.

src/libutil/url.hh

@@ -7,9 +7,8 @@ namespace nix {
 
 struct ParsedURL
 {
-    std::string url;
     /// URL without query/fragment
-    std::string base;
+    std::string base; // FIXME: remove
     std::string scheme;
     std::optional<std::string> authority;
     std::string path;
@@ -26,6 +25,8 @@ struct ParsedURL
     ParsedURL canonicalise();
 };
 
+std::ostream & operator << (std::ostream & os, const ParsedURL & url);
+
 MakeError(BadURL, Error);
 
 std::string percentDecode(std::string_view in);