Remove subcategories from conference user (#213)

app/models/conference_user.rb

@@ -4,11 +4,6 @@ class ConferenceUser < ActiveRecord::Base
   belongs_to :conference
   belongs_to :user
 
-  has_many :conference_user_subcategories
-  has_many :subcategories, through: :conference_user_subcategories
-
-  accepts_nested_attributes_for :conference_user_subcategories, allow_destroy: true
-
   validates :conference, :user, :role, presence: true
   validate :user_role_is_crew
   validate :role_is_valid