Added EmailsDownload controller and routes

Removed original method to return emails file from Newsletters controller and NewsletterZip class, included `rubyzip` gem that's no longer necessary.

app/controllers/admin/emails_download_controller.rb

@@ -0,0 +1,18 @@
+class Admin::EmailsDownloadController < Admin::BaseController
+  def index
+  end
+
+  def generate_csv
+    users_segment = params[:users_segment]
+    filename = t("admin.segment_recipient.#{users_segment}")
+
+    csv_file = users_segment_emails_csv(users_segment)
+    send_data csv_file, filename: "#{filename}.csv"
+  end
+
+  private
+
+  def users_segment_emails_csv(users_segment)
+    UserSegments.send(users_segment).pluck(:email).to_csv
+  end
+end

app/controllers/admin/newsletters_controller.rb

@@ -44,12 +44,6 @@ class Admin::NewslettersController < Admin::BaseController
     redirect_to admin_newsletters_path, notice: t("admin.newsletters.delete_success")
   end
 
-  def users
-    zip = NewsletterZip.new('emails')
-    zip.create
-    send_file(File.join(zip.path), type: 'application/zip')
-  end
-
   def deliver
     @newsletter = Newsletter.find(params[:id])
     Mailer.newsletter(@newsletter).deliver_later