Remove poltergeist gem, which is unused

Gemfile

@@ -111,7 +111,6 @@ group :development, :test do
   gem 'factory_bot_rails'
   gem 'capybara'
   gem 'rspec-rails', '~> 3.6'
-  gem 'poltergeist'
 
   # debug
   gem 'pry', '0.10.1'

spec/rails_helper.rb

@@ -2,7 +2,6 @@ ENV['RAILS_ENV'] ||= 'test'
 require 'spec_helper'
 require File.expand_path('../../config/environment', __FILE__)
 require 'rspec/rails'
-require 'capybara/poltergeist'
 require 'paper_trail/frameworks/rspec'
 require 'money-rails/test_helpers'
 require 'support/requests/session_helpers'

spec/support/capybara.rb

@@ -4,5 +4,3 @@ RSpec.configure do |config|
   config.include CapybaraViewMacros, type: :view
   config.include CapybaraViewMacros, type: :presenter
 end
-
-Capybara.javascript_driver = :poltergeist