Send a plaintext link to the mapreduce console in fluent style

The link was previously being sent using a JS redirect, which doesn't work
because the endpoints that trigger mapreduces can only be hit from the command
line (because they require auth). This commit switches the link to be in
plaintext and renders the full URL instead of just the path, so that clicking it
directly from the terminal works.

This also improves how these links are sent from callsites by using a fluent
style.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228764606

java/google/registry/request/Response.java

@@ -51,12 +51,4 @@ public interface Response {
    * @see HttpServletResponse#setDateHeader(String, long)
    */
   void setDateHeader(String header, DateTime timestamp);
-
-  /**
-   * Sends a JavaScript redirect HTTP response.
-   *
-   * GAE handles a HTTP 302 status as an error, so using this is helpful for responses that might
-   * sometimes be consumed by GAE code, since it performs a redirect while also returning HTTP 200.
-   */
-  void sendJavaScriptRedirect(String redirectUrl);
 }