Fix bug in named url middleware when running at non-root path

The most notable change here is the removal of the conditional in
process_request. I don't know why we were preferring REQUEST_URI over
PATH_INFO. When the app is running at /, they are always the same as far as I
can tell. However, when using SCRIPT_NAME, this was incorrectly setting path and
path_info to /myprefix/myprefix/.

awx/main/middleware.py

@@ -180,11 +180,7 @@ class URLModificationMiddleware(MiddlewareMixin):
         return '/'.join(url_units)
 
     def process_request(self, request):
-        if hasattr(request, 'environ') and 'REQUEST_URI' in request.environ:
-            old_path = urllib.parse.urlsplit(request.environ['REQUEST_URI']).path
-            old_path = old_path[request.path.find(request.path_info) :]
-        else:
-            old_path = request.path_info
+        old_path = request.path_info
         new_path = self._convert_named_url(old_path)
         if request.path_info != new_path:
             request.environ['awx.named_url_rewritten'] = request.path