Delete unused description field from premium/reserved list entities

It isn't used now, and as far as I can tell it was never used for anything, so
get rid of it.  We won't be using it in our new Cloud SQL schema anyway.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=242501877

java/google/registry/model/registry/label/BaseDomainLabelList.java

@@ -64,8 +64,6 @@ public abstract class BaseDomainLabelList<T extends Comparable<?>, R extends Dom
 
   DateTime lastUpdateTime;
 
-  String description;
-
   public String getName() {
     return name;
   }
@@ -182,11 +180,6 @@ public abstract class BaseDomainLabelList<T extends Comparable<?>, R extends Dom
       return thisCastToDerived();
     }
 
-    public B setDescription(String description) {
-      getInstance().description = description;
-      return thisCastToDerived();
-    }
-
     @Override
     public T build() {
       checkArgument(!isNullOrEmpty(getInstance().name), "List must have a name");