Remove an unnecessary ERB pass over fetched templates.

The only templates returned from static with ERB tags in them are the
.raw ones, because they're used by various processors (that do their own
ERB processing).  This block is therefore only running plain html
through ERB, which is pointless.
Merge pull request #58 from alphagov/remove_unnecessary_erb_pass

Remove an unnecessary ERB pass over fetched templates.