fix(接口测试): 接口参数添加mock数据时清空历史函数

--bug=1020194 --user=宋天阳 [接口测试]
github#19929接口参数设置中添加函数后不点保存，点击下一个参数的小铅笔，历史函数不可消除，导致预览还会加上函数；重新进入场景编辑参数，无此问题
https://www.tapd.cn/55049933/s/1320348

api-test/frontend/src/business/definition/components/ApiVariable.vue

@@ -75,7 +75,7 @@
                     value-key="name"
                     highlight-first-item
                     @select="change">
-                    <i slot="suffix" class="el-input__icon el-icon-edit pointer" @click="advanced(item)"></i>
+                    <i slot="suffix" class="el-input__icon el-icon-edit pointer" @click="advanced(scope.row)"></i>
                   </el-autocomplete>
                 </div>
                 <div v-else-if="isActive && scope.row.type === 'file'">

api-test/frontend/src/business/definition/components/ApiVariableAdvance.vue

@@ -416,6 +416,7 @@ export default {
       this.operatingElements = this.stepFilter.get('ALL');
     },
     open() {
+      this.itemValuePreview = null;
       this.itemValue = null;
       if (this.scenarioDefinition != undefined) {
         // 标识为场景编辑入口进入