Clean up BaseUser class by removing unused code

Removed unused import and SerializedName annotation.

Author: Justintime50

src/main/java/com/easypost/model/BaseUser.java

@@ -1,7 +1,6 @@
 package com.easypost.model;
 
 import java.util.List;
-import com.google.gson.annotations.SerializedName;
 import lombok.Getter;
 
 @Getter
@@ -22,7 +21,5 @@ public class BaseUser extends EasyPostResource {
     private String insuranceFeeRate;
     private String insuranceFeeMinimum;
     private List<User> children;
-
-    @SerializedName("api_keys")
     private List<ApiKey> apiKeys;
 }