Delete mapreduce entity cleanup util

This is obsoleted by the upcoming Registry 3.0 migration, after which we will be
using neither the App Engine Mapreduce library nor Cloud Datastore.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=212864845

java/google/registry/env/common/backend/WEB-INF/web.xml

@@ -210,12 +210,6 @@
     <url-pattern>/_dr/task/pollBigqueryJob</url-pattern>
   </servlet-mapping>
 
-  <!-- Cleans up old mapreduce entities. -->
-  <servlet-mapping>
-    <servlet-name>backend-servlet</servlet-name>
-    <url-pattern>/_dr/task/mapreduceEntityCleanup</url-pattern>
-  </servlet-mapping>
-
   <!-- Fans out a cron task over an adjustable range of TLDs. -->
   <servlet-mapping>
     <servlet-name>backend-servlet</servlet-name>