InputNumber: remove undocumented slots (#11794)

packages/input-number/src/input-number.vue

@@ -40,12 +40,6 @@
       @blur="handleBlur"
       @focus="handleFocus"
       @change="handleInputChange">
-      <template slot="prepend" v-if="$slots.prepend">
-        <slot name="prepend"></slot>
-      </template>
-      <template slot="append" v-if="$slots.append">
-        <slot name="append"></slot>
-      </template>
     </el-input>
   </div>
 </template>