Remove PDF related dependencies

WickedPDF may be causing the 'fatal (machine stack overflow in critical region)' error that we're receiving. See mileszs/wicked_pdf#818

app/helpers/spree/admin/base_helper_decorator.rb

@@ -12,10 +12,6 @@ def form_action(insight, insight_type)
       def page_selector_options
         [5, 10, 20, 30, 45, 60]
       end
-
-      def pdf_logo(image_path = Spree::Config[:logo])
-        wicked_pdf_image_tag image_path, class: 'logo'
-      end
     end
   end
 end

config/initializers/mime_types.rb

@@ -1,2 +1 @@
 Mime::Type.register "application/xls", :xls
-# Mime::Type.register "application/pdf", :pdf

lib/spree_admin_insights/engine.rb

@@ -1,7 +1,6 @@
 module SpreeAdminInsights
   class Engine < Rails::Engine
     require 'spree/core'
-    require 'wicked_pdf'
     require 'csv'
 
     isolate_namespace Spree
@@ -12,8 +11,6 @@ class Engine < Rails::Engine
       g.test_framework :rspec
     end
 
-    config.assets.precompile << 'spree/backend/override_pdf.css'
-
     def self.activate
       Dir.glob(File.join(File.dirname(__FILE__), '../../app/**/*_decorator*.rb')) do |c|
         Rails.configuration.cache_classes ? require(c) : load(c)

spree_admin_insights.gemspec

@@ -35,6 +35,4 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'simplecov'
   s.add_development_dependency 'sqlite3'
   s.add_development_dependency 'shoulda-matchers'
-  s.add_dependency 'wicked_pdf'
-  s.add_dependency 'wkhtmltopdf-binary'
 end