Temporarily revert "FEATURE: Support [description|attachment](upload://<short-sha>) in MD. (#7603)"

This reverts commit b1d3c678ca39cf7f09ac3eb257c7153d4863a2a9.

We need to make sure post_upload records are correctly stored.

test/javascripts/acceptance/composer-attachment-test.js.es6

@@ -1,39 +0,0 @@
-import { acceptance } from "helpers/qunit-helpers";
-
-acceptance("Composer Attachment", {
-  loggedIn: true,
-  pretend(server, helper) {
-    server.post("/uploads/lookup-urls", () => {
-      return helper.response([
-        {
-          short_url: "upload://asdsad.png",
-          url: "/uploads/default/3X/1/asjdiasjdiasida.png",
-          short_path: "/uploads/short-url/asdsad.png"
-        }
-      ]);
-    });
-  }
-});
-
-QUnit.test("attachments are cooked properly", async assert => {
-  await visit("/t/internationalization-localization/280");
-  await click("#topic-footer-buttons .btn.create");
-
-  await fillIn(".d-editor-input", "[test](upload://abcdefg.png)");
-
-  assert.equal(
-    find(".d-editor-preview:visible")
-      .html()
-      .trim(),
-    '<p><a href="/404">test</a></p>'
-  );
-
-  await fillIn(".d-editor-input", "[test|attachment](upload://asdsad.png)");
-
-  assert.equal(
-    find(".d-editor-preview:visible")
-      .html()
-      .trim(),
-    '<p><a href="/uploads/short-url/asdsad.png" class="attachment">test</a></p>'
-  );
-});