This will silence deprecation warnings.
Most of the test can be changed from `render :text` to render `:plain`
or `render :body` right away. However, there are some tests that needed
to be fixed by hand as they actually assert the default Content-Type
returned from `render :body`.
This is another take at #14384 as we decided to wait until `master` is
targeting Rails 5.0. This commit is implementation-complete, as it
guarantees that all the public methods on the hash-inherited Parameters
are still working (based on test case). We can decide to follow-up later
if we want to remove some methods out from Parameters.
ParamsWrapper was initially removed from API controllers according to
the following discusision:
https://github.com/rails-api/rails-api/issues/33
However, we're including it again so Rails API devs can decide
whether to enable or disable it.
