There is no way to turn off the code injection of the Live Preview function, it would not work as described in the documentation if that were possible.
You have two methods of accessing the old Preview in Browser (now called Open in Browser), one is as Ben shows, when your documents are set as tabs in your workspace. The other, when you have floating documents, is to right click the file in the Files window and choose the same menu option "Open in Browser", see below...
If you feel that is not the way things should be done, be sure to let the dev team know by submitting a feature request from within DW under Help > Submit Bug Report/Feature Request. If enough people are asking for the same, there's a good chance Adobe will add the old functionality back as the default, or give us an option to add the keyboard shortcut to the current Open in Browser function.