Remove default styles and make it headless

[fayazara]

I see that there are a few default styles added in this, which actually make the icons behave differently than it should. https://github.com/nuxt-modules/icon/blob/4ecfd3a4672505799aa040176da9bf737f6b5f9a/src/runtime/Icon.vue#LL56-L61C2

<style scoped>
.icon {
  display: inline-block;
  vertical-align: middle;
}
</style>