Remove toString() method on Result.Code and fix metrics recording

We almost certainly had intended to record a String representation of the
numeric Code all along, but a bad toString() method on the enum resulted
in the wrong thing happening.  This is more evidence of why overriding
toString() on enums is bad.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133583683

java/google/registry/model/eppoutput/Result.java

@@ -150,11 +150,6 @@ public class Result extends ImmutableObject {
     public boolean isSuccess() {
       return code < 2000;
     }
-
-    @Override
-    public String toString() {
-      return String.format("{code:'%s', msg:'%s', msgLang:'%s'}", code, msg, msgLang);
-    }
   }
 
   /** The result code for this result. This is always present. */