Remove Ransack from Exercise edit for tags

* Also improve Ransack usage of attributes and associations

app/models/user.rb

@@ -41,4 +41,8 @@ class User < ApplicationRecord
   def to_s
     displayname
   end
+
+  def self.ransackable_attributes(_auth_object = nil)
+    %w[name email external_id consumer_id role]
+  end
 end