Fix duplicate meta charset declaration

Deleted duplicate meta charset attribute declaration in ```/_layouts/defaults.html```

In HTML5 (as declared by jekyll-now doctype),  
```html
<meta charset="utf-8" />
``` 
is equivalent to 
```html
 <meta content='text/html; charset=utf-8' http-equiv='Content-Type'>
```

- Deleted the longer version as the shortcut is preferrable
- Ref [MetaCharsetAttribute](https://code.google.com/p/doctype-mirror/wiki/MetaCharsetAttribute)