refactor(PaginationField): 移除不必要的占位元素

清理了未使用的占位div及其相关样式，简化DOM结构

 <!--
  * @Date: 2025-11-18 16:17:40
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-11-20 17:55:05
+ * @LastEditTime: 2025-11-20 17:56:14
  * @FilePath: /data-table/src/components/PaginationField/index.vue
  * @Description: 分页组件
 -->
@@ -21,7 +21,6 @@
       <van-button v-if="showSubmit" round type="primary" class="btn" @click="onSubmit">{{ submitButton.text }}</van-button>
     </div>
   </div>
-  <div class="placeholder" />
 </template>
 
 <script setup>
@@ -103,8 +102,4 @@ const onSubmit = () => emit('submit')
     }
   }
 }
-
-.placeholder {
-  height: 3.75rem;
-}
 </style>