Revert "Use Meteor.absoluteUrl again in dynamic-import fetchMissing function."

This reverts commit 3b77bb5197.

Should fix #9888.

Sending dynamic import() requests to any origin other than location.host
causes some browsers to send a preflight CORS request ( method:OPTIONS) to
verify that the server allows the request, which was causing problems
because the dynamic import() server expects method:POST.

packages/dynamic-import/client.js

@@ -121,7 +121,11 @@ var fetchURL = require("./common.js").fetchURL;
 
 function fetchMissing(missingTree) {
   return new Promise(function (resolve, reject) {
-    HTTP.call("POST", Meteor.absoluteUrl(fetchURL), {
+    // Always match the protocol (http or https) and the domain:port of
+    // the current page.
+    var url = "//" + location.host + fetchURL;
+
+    HTTP.call("POST", url, {
       query: secretKey ? "key=" + secretKey : void 0,
       data: missingTree
     }, function (error, result) {