Cut over to generating new HMAC-based XSRF tokens

This is the second step of migrating to our new XSRF token format.  The
first step ([] made validate() start accepting new tokens
(basically, dual-read).  This step cuts over our "writing" to write the
new token format.  The third and final step will drop support for
validating the old token format (back to single-read).  We'll do that
in a subsequent push so that we don't invalidate all the current XSRF
tokens that people might have in their browsers.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=149790648

java/google/registry/tools/AppEngineConnection.java

@@ -66,7 +66,7 @@ class AppEngineConnection implements Connection {
       memoize(new Supplier<String>() {
         @Override
         public String get() {
-          return xsrfTokenManager.generateLegacyToken("admin", getUserId());
+          return xsrfTokenManager.generateToken(getUserId());
         }});
 
   @Override