Remove `#build_original_fullpath` method

Removing `#build_original_fullpath` because it is no longer
used by the Rails' source code or called in the `#call` method becasue
the previous commit now uses `fullpath` from Rack.

The method was nodoc'ed so it's safe to remove.

NOTE: I did this as a separate commit so if this does cause a problem
with engines etc reverting is easy.

railties/lib/rails/application.rb

@@ -505,11 +505,6 @@ def default_middleware_stack #:nodoc:
       default_stack.build_stack
     end
 
-    def build_original_fullpath(env) #:nodoc:
-      req = ActionDispatch::Request.new env
-      env["ORIGINAL_FULLPATH"] = req.fullpath
-    end
-
     def validate_secret_key_config! #:nodoc:
       if secrets.secret_key_base.blank?
         ActiveSupport::Deprecation.warn "You didn't set `secret_key_base`. " +

railties/test/application/build_original_fullpath_test.rb

-require "abstract_unit"
-
-module ApplicationTests
-  class BuildOriginalPathTest < ActiveSupport::TestCase
-    def test_include_original_PATH_info_in_ORIGINAL_FULLPATH
-      env = { 'PATH_INFO' => '/foo/' }
-      assert_equal "/foo/", Rails.application.send(:build_original_fullpath, env)
-    end
-
-    def test_include_SCRIPT_NAME
-      env = {
-        'SCRIPT_NAME' => '/foo',
-        'PATH_INFO' => '/bar'
-      }
-
-      assert_equal "/foo/bar", Rails.application.send(:build_original_fullpath, env)
-    end
-
-    def test_include_QUERY_STRING
-      env = {
-        'PATH_INFO' => '/foo',
-        'QUERY_STRING' => 'bar',
-      }
-      assert_equal "/foo?bar", Rails.application.send(:build_original_fullpath, env)
-    end
-  end
-end