Revert "Its ideal to set Vary: Accept-Encoding, irrespective of whether gzipped version exists or not. This is helpful for CDN's to later distinguish assets, based on previous, current copies and introduced gzip version if any."

This reverts commit 067c52f608.

Conversation: https://github.com/rails/rails/pull/23120#issuecomment-173007011

actionpack/lib/action_dispatch/middleware/static.rb

@@ -65,7 +65,7 @@ module ActionDispatch
         status, headers, body = @file_server.call(request.env)
       end
 
-      headers['Vary'] = 'Accept-Encoding'
+      headers['Vary'] = 'Accept-Encoding' if gzip_path
 
       return [status, headers, body]
     ensure

actionpack/test/dispatch/static_test.rb

@@ -233,7 +233,7 @@ module StaticTests
     def assert_html(body, response)
       assert_equal body, response.body
       assert_equal "text/html", response.headers["Content-Type"]
-      assert_not_nil response.headers["Vary"]
+      assert_nil response.headers["Vary"]
     end
 
     def get(path, headers = {})