Move prober deletion action to backend module

Also creates a new package named 'batch' to house it.

TESTED=I deployed it to alpha, sent a POST request to the task URL, and it
successfully ran the [].

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134332999

java/google/registry/module/backend/BUILD

@@ -20,6 +20,7 @@ java_library(
         "//third_party/java/jsr330_inject",
         "//third_party/java/servlet/servlet_api",
         "//java/google/registry/backup",
+        "//java/google/registry/batch",
         "//java/google/registry/bigquery",
         "//java/google/registry/billing",
         "//java/google/registry/config",