Remove ActionView template handler

@shopify/liquid for review

## Problem

Fixes issue #21 where tobi said:
> Liquid isn't a very good template engine for rails projects. It's optimized to work in a hostile environment where you cannot trust the people who write the templates. This is different from a development environment in which you should trust your designers and developers who create the templates.
>
> I feel that by including a init.rb we encurage a usage of Liquid that is different from it's actual intend.

It sounds like this usage is also broken in rails 3 according to issue #125.

## Solution

Now is a good time to remove this code because the next release of code in master will be a major release.