C++: Remove an unecessary unresolveElement.

As far as I can see, `@file` is not a `@usertype`, so this shouldn't be needed.

cpp/ql/src/semmle/code/cpp/XML.qll

@@ -20,7 +20,7 @@ abstract class XMLLocatable extends @xmllocatable {
     string filepath, int startline, int startcolumn, int endline, int endcolumn
   ) {
     exists(File f, Location l | l = this.getLocation() |
-      locations_default(l, unresolveElement(f), startline, startcolumn, endline, endcolumn) and
+      locations_default(l, f, startline, startcolumn, endline, endcolumn) and
       filepath = f.getAbsolutePath()
     )
   }