Remove shims that force deprecated form of methods

We have two spec helper files that provide shims for deprecated forms of some methods:

• spec/support/http_method_shims.rb
• spec/support/controller_helpers.rb

The shims implemented in these were useful when working with Rails 4.2, which we don't support any more.

Right now, they force us to use a style that is deprecated and triggers a RuboCop warning Rails/HttpPositionalArguments. Example from the RuboCop documentation for this rule[1]:

# bad
get :new, { user_id: 1}

# good
get :new, params: { user_id: 1 }
get :new, **options

In this PR I remove the shims and convert all usages to the modern form.

[1] https://www.rubydoc.info/gems/rubocop-rails/RuboCop/Cop/Rails/HttpPositionalArguments