dispose tech after turning event bindings off

Switching the disposal order so that event bindings are turned off before tech.dispose() is called. Previously, bindings to timeupdate that touched the tech element would error out, as the element was destroyed before a timeupdate event was triggered in [player.js:403](https://github.com/videojs/video.js/blob/8a05aa11a13eeccffaff39d5579214c908b8aa13/src/js/player.js#L403)