stop directly setting headers on the controller

again, since we are going through the test harness, all this is done
for us.

actionpack/lib/action_controller/metal/testing.rb

@@ -2,11 +2,6 @@ module ActionController
   module Testing
     extend ActiveSupport::Concern
 
-    # TODO : Rewrite tests using controller.headers= to use Rack env
-    def headers=(new_headers)
-      @_response.headers.replace(new_headers)
-    end
-
     # Behavior specific to functional tests
     module Functional # :nodoc:
       def set_response!(request)

actionpack/test/controller/send_file_test.rb

@@ -27,7 +27,6 @@ def test_send_file_headers_bang
       :filename => 'filename'
     }
 
-    self.headers = {}
     send_data "foo", options
   end
 
@@ -38,34 +37,27 @@ def test_send_file_headers_with_disposition_as_a_symbol
       :filename => 'filename'
     }
 
-    self.headers = {}
     send_data "foo", options
   end
 
   def test_send_file_headers_with_mime_lookup_with_symbol
-    options = {
-      :type => :png
-    }
+    options = { :type => :png }
 
-    self.headers = {}
     send_data "foo", options
   end
 
   def test_send_file_headers_with_bad_symbol
     options = { :type => :this_type_is_not_registered }
-    self.headers = {}
     send_data "foo", options
   end
 
   def test_send_file_headers_with_nil_content_type
     options = { :type => nil }
-    self.headers = {}
     send_data "foo", options
   end
 
   def test_send_file_headers_guess_type_from_extension
     options = { :filename => params[:filename] }
-    self.headers = {}
     send_data "foo", options
   end