Reapply "Destroy equivalent filters upon resource removal"

This reverts commit 5e09fddbe0.

app/models/filter/resources.rb

@@ -12,6 +12,8 @@ module Filter::Resources
     kind = resource.class.model_name.plural
     send "#{kind}=", send(kind).without(resource)
     empty? ? destroy! : save!
+  rescue ActiveRecord::RecordNotUnique
+    destroy!
   end
 
   def buckets

test/models/filter_test.rb

@@ -89,6 +89,11 @@ class FilterTest < ActiveSupport::TestCase
     assert_includes filter.as_params[:bucket_ids], buckets(:writebook).id
     assert_includes filter.buckets, buckets(:writebook)
 
+    users(:david).filters.create! tag_ids: [ tags(:mobile).id, tags(:web).id ], bucket_ids: [ buckets(:writebook).id ]
+    assert_difference "Filter.count", -1 do
+      tags(:web).destroy!
+    end
+
     assert_changes "filter.reload.updated_at" do
       tags(:mobile).destroy!
     end