Revert "AP-314: ensure latest dash.js loads"

This reverts commit 6499474.

Upstream dash.js has fixed their URL resolution, so this isn't needed
any more.

See-also: avplayer#8
Ref: AP-314

Author: awilfox

app/views/player/_player_head_additional.erb

@@ -38,8 +38,6 @@
             // (when the HLS stream contains WebVTT captions)
             hls: { enableWebVTT: false },
             iconSprite: "/assets/icons/mejs-controls.svg",
-            // workaround for AP-314
-            dash: { path: "https://cdn.dashjs.org/latest/legacy/umd/dash.all.min.js" },
             success: function (mediaElement, originalNode, instance) {
                 if (typeof dashjs !== "undefined") {
                     // workaround for mediaelement/mediaelement#2964