perf: remove src directory from npm module (#6072)

`src` directory is not used by node package. Removing this directory reduces size of `.tgz` package by 112kb and saves 840kb on each node projects, where vue.js is installed

package.json

@@ -7,7 +7,6 @@
   "unpkg": "dist/vue.js",
   "typings": "types/index.d.ts",
   "files": [
-    "src",
     "dist/*.js",
     "types/*.d.ts"
   ],