Remove uses of ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES

When running the test suite on Rails 5 I'm getting quite a few errors that say: uninitialized constant ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES.

This is because the constant was removed in Rails 5.

Thankfully we use it in only 2 places:

$ git grep 'TRUE_VALUES'
app/models/notification_setting.rb:      events[event] = ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES.include?(events[event])
app/models/service.rb:          ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES.include?(#{arg})