Partially revert "ActionDispatch should require as little of ActiveSupport as possible"

Removes load path change from commit bb153f42.

actionpack/lib/action_dispatch.rb

@@ -21,6 +21,8 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #++
 
+activesupport_path = File.expand_path('../../../activesupport/lib', __FILE__)
+$:.unshift(activesupport_path) if File.directory?(activesupport_path) && !$:.include?(activesupport_path)
 require 'active_support'
 require 'active_support/dependencies/autoload'