Do not add format key to request_params

I did this change but it is affecting how the request params end up
after being processed by the router.

To be in the safe side, I just take the format from the extension in the
URL when is not present in those params and it's being used only for the
`Request#formats` method

actionpack/lib/action_dispatch/http/mime_negotiation.rb

@@ -67,6 +67,8 @@ def formats
 
           v = if params_readable
             Array(Mime[parameters[:format]])
+          elsif format_from_path_extension
+            [Mime[format_from_path_extension]]
           elsif use_accept_header && valid_accept_header
             accepts
           elsif xhr?
@@ -160,6 +162,13 @@ def valid_accept_header
       def use_accept_header
         !self.class.ignore_accept_header
       end
+
+      def format_from_path_extension
+        path = @env['action_dispatch.original_path'] || @env['PATH_INFO']
+        if match = path && path.match(/\.(\w+)\z/)
+          match.captures.first
+        end
+      end
     end
   end
 end

actionpack/lib/action_dispatch/http/parameters.rb

@@ -41,9 +41,9 @@ def path_parameters=(parameters) #:nodoc:
       # Returns a hash with the \parameters used to form the \path of the request.
       # Returned hash keys are strings:
       #
-      #   {'action' => 'my_action', 'controller' => 'my_controller', format => 'html'}
+      #   {'action' => 'my_action', 'controller' => 'my_controller'}
       def path_parameters
-        get_header(PARAMETERS_KEY) || default_path_parameters
+        get_header(PARAMETERS_KEY) || {}
       end
 
       private
@@ -66,21 +66,6 @@ def parse_formatted_parameters(parsers)
       def params_parsers
         ActionDispatch::Request.parameter_parsers
       end
-
-      def default_path_parameters
-        if format = format_from_path_extension
-          { format: format }
-        else
-          {}
-        end
-      end
-
-      def format_from_path_extension
-        path = @env['action_dispatch.original_path'] || @env['PATH_INFO']
-        if match = path && path.match(/\.(\w+)\z/)
-          match.captures.first
-        end
-      end
     end
   end
 end

actionpack/test/dispatch/routing_test.rb

@@ -3272,7 +3272,6 @@ def test_multiple_positional_args_with_the_same_name
     expected_params = {
       controller: 'downloads',
       action:     'show',
-      format:     'tar',
       id:         '1'
     }