Avoid unnecessary monkey patching.

* Removing the root on decoding was added to ActiveResource 3.1, so
  only needs to be patched for 3.0.
* The encode patch isn't needed for ActiveModel 3.2, since ActiveResource
  passes :root to as_json, and in 3.2 :root is used even when
  include_root_in_json is false.
* The as_json patch was compensating for the encode patch for ActiveModel
  3.2, so this patch isn't necessary by avoiding patching encode for this
  version.
* The encode patch is ShopifyAPI::Base specific, since we set
  include_root_in_json to false and add the root manually. We should
  avoid side-effects for other APIs.