fix: Previously set onGlobalSetup executes for next requests.

[vaiil]

🐛 The bug
Previously set onGlobalSetup executes for next requests.

🛠️ To reproduce
Steps to reproduce the behavior:
Make new plugin with following code:

import { onGlobalSetup } from "@nuxtjs/composition-api";
export default () => {
  console.log("Plugin initialized");
  onGlobalSetup(() => {
    console.log("Setup runned");
  });
};

and try to reload page few times.
Log would be:

Plugin initialized
Setup runned
Plugin initialized
Setup runned
Setup runned
Plugin initialized
Setup runned
Setup runned
Setup runned

Or you can visit codesandbox with the bug:
https://codesandbox.io/s/tender-dream-6wjvf?file=/plugins/custom-plugin.js:0-183

🌈 Expected behaviour
One call onGlobalSetup for each request.

ℹ️ Additional context
Node version 14
Production build
Latest nuxt (2.14.6) and @nuxtjs/composition-api (0.13.1)