[svelte] preprocesser adds unnecessary classes

[s0kil]

From:

<svelte:head>
  <title>Home | Website</title>
</svelte:head>

Into:

<svelte:head class={__styled__.styles["__svelte:head"]} style={__styles__.$$style}>
  <title class={__styled__.styles["__title"]}>Home | Website</title>
</svelte:head>

This is related to #97

The preprocesser should skip any tags that start with <svelte: /> such as:

• <svelte:self>
• <svelte:component>
• <svelte:window>
• <svelte:body>
• <svelte:head>
• <svelte:options>

Non of these tags can be styled.