refactor: clean babel config when invoking

Author: yyx990803

packages/@vue/cli-plugin-babel/generator.js

@@ -1,4 +1,10 @@
 module.exports = api => {
+  // Most likely you want to overwrite the whole config to ensure it's working
+  // without conflicts, e.g. for a project that used Jest without Babel.
+  // It should be rare for the user to have their own special babel config
+  // without using the Babel plugin already.
+  delete api.generator.files['babel.config.js']
+
   api.extendPackage({
     babel: {
       presets: ['@vue/app']