remove legacy tracking param

app/controllers/api/submitter_email_clicks_controller.rb

@@ -8,8 +8,7 @@ module Api
     def create
       submitter = Submitter.find_by!(slug: params[:submitter_slug])
 
-      if params[:t] == SubmissionEvents.build_tracking_param(submitter, 'click_email') ||
-         params[:t] == SubmissionEvents.build_tracking_param_legacy(submitter, 'click_email')
+      if params[:t] == SubmissionEvents.build_tracking_param(submitter, 'click_email')
         SubmissionEvents.create_with_tracking_data(submitter, 'click_email', request)
       end
 

lib/submission_events.rb

@@ -20,12 +20,6 @@ module SubmissionEvents
 
   module_function
 
-  def build_tracking_param_legacy(submitter, event_type = 'click_email')
-    Base64.urlsafe_encode64(
-      [submitter.slug, event_type].join(':')
-    ).first(TRACKING_PARAM_LENGTH)
-  end
-
   def build_tracking_param(submitter, event_type = 'click_email')
     Base64.urlsafe_encode64(
       Digest::SHA1.digest([submitter.slug, event_type, Rails.application.secret_key_base].join(':'))