Remove a DAVE test that seems invalid to me (refs: #12005).

The page that's being used for this
test (https://tails.boum.org/install/debian/usb/) is DAVE-enabled. It doesn't
display any link to the ISO, and DAVE picks a mirror itself, so that should work
regardless of JavaScript settings. So I'm not surprised that we've been reported
several time that this test doesn't pass :)

wiki/src/contribute/release_process/test.mdwn

@@ -310,9 +310,8 @@ You *really* have to reboot between each language.
 * Visit <https://tails.boum.org/install/debian/usb> in a Firefox-based
   browser. Verify that you can install the Firefox Addon. Start
   downloading a Tails image and copy the used mirror URL.
-  - The URL should only start with dl.amnesia.boum.org if Javascript
-    is disabled in your browser (requires a restart!). Otherwise it should
-    contain a mirror URL from <https://tails.boum.org/mirrors.json>
+  - The URL should contain a mirror URL from
+    <https://tails.boum.org/mirrors.json>.
   - Verify that pausing and resuming the download from this URL works.
   - Verify that when you start the download, you can see it appear in
     the download list (Ctrl+Shift+Y).