Move simplecov config into rails_helper (#30302)

.simplecov

@@ -1,22 +0,0 @@
-# frozen_string_literal: true
-
-if ENV['CI']
-  require 'simplecov-lcov'
-  SimpleCov::Formatter::LcovFormatter.config.report_with_single_file = true
-  SimpleCov.formatter = SimpleCov::Formatter::LcovFormatter
-else
-  SimpleCov.formatter = SimpleCov::Formatter::HTMLFormatter
-end
-
-SimpleCov.start 'rails' do
-  enable_coverage :branch
-
-  add_filter 'lib/linter'
-
-  add_group 'Libraries', 'lib'
-  add_group 'Policies', 'app/policies'
-  add_group 'Presenters', 'app/presenters'
-  add_group 'Serializers', 'app/serializers'
-  add_group 'Services', 'app/services'
-  add_group 'Validators', 'app/validators'
-end