Remove old json logging from flows

This was meant for log replay and has long been ignored/useless.
As part of this, remove execution time from EppResponse since this
was the only thing consuming it.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=137293734

java/google/registry/flows/Flow.java

@@ -86,7 +86,6 @@ public abstract class Flow {
         .setMessageQueueInfo(messageQueueInfo)
         .setResData(responseData)
         .setExtensions(responseExtensions)
-        .setExecutionTime(now)
         .build());
   }