Don't generate redundant <meta http-equiv=content-type>.

Quoting from the HTML specification[1]:

  A document must not contain both a meta element with an http-equiv attribute
  in the Encoding declaration state and a meta element with the charset
  attribute present.

So we remove the <meta> with the http-equiv attribute from our template.

[1]: https://html.spec.whatwg.org/multipage/semantics.html#attr-meta-http-equiv-content-type

src/theme/index.hbs

@@ -15,7 +15,6 @@
         <!-- Custom HTML head -->
         {{> head}}
 
-        <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
         <meta name="description" content="{{ description }}">
         <meta name="viewport" content="width=device-width, initial-scale=1">
         <meta name="theme-color" content="#ffffff" />