DEV: Drop WithServiceHelper

This patch removes the `with_service` helper from the code base.
Instead, we can pass a block with actions directly to the `.call` method
of a service.

This simplifies how to use services:
- use `.call` without a block to run the service and get its result
  object.
- use `.call` with a block of actions to run the service and execute
  arbitrary code depending on the service outcome.

It also means a service is now “self-contained” and can be used anywhere
without having to include a helper or whatever.

app/helpers/with_service_helper.rb

@@ -1,27 +0,0 @@
-# frozen_string_literal: true
-
-module WithServiceHelper
-  def result
-    @_result
-  end
-
-  # @param service [Class] A class including {Service::Base}
-  # @param dependencies [kwargs] Any additional params to load into the service context,
-  #   in addition to controller @params.
-  def with_service(service, **dependencies, &block)
-    object = self
-    ServiceRunner.call(
-      service,
-      object,
-      **dependencies,
-      &proc { instance_exec(&(block || proc {})) }
-    )
-  end
-
-  def run_service(service, dependencies)
-    params = self.try(:params) || ActionController::Parameters.new
-
-    @_result =
-      service.call(params.to_unsafe_h.merge(guardian: self.try(:guardian) || nil, **dependencies))
-  end
-end