chore: 删除无效代码

packages/uni-mp-weixin/lib/independent-plugins/add-weixin-mp-runtime-plugin.js

 const fs = require('fs-extra');
-const path = require('path');
 const { generateAsset } = require('./utils');
 const t = require('@babel/types');
 const babelGenerator = require('@babel/generator');

packages/uni-mp-weixin/lib/independent-plugins/inject-main-css-to-independent-plugin.js

@@ -35,7 +35,6 @@ function copyWeuiCssToIndependent (independentRoot) {
 function tryInsertWeuiCss (independentRoot, originalWxssStr) {
     const manifestConfig = process.UNI_MANIFEST;
     const weixinConfig = manifestConfig['mp-weixin'] || {};
-    const independentSwitch = !!weixinConfig.independent;
     // 如果使用了weui，则需要注入weui样式
     const useExtendedWeUi = !!(weixinConfig.useExtendedLib || {}).weui;