Remove RubyEventStore from mutation tests
Remove RubyEventStore from mutation tests

Until we kill the mutants generated by the code in Event initializer:

```ruby
  8       singleton_class = (class << self; self; end)
  9       attributes.each do |key, value|
  10         singleton_class.send(:define_method, key) { value }
  11      end
```

mpraglowski/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,RailsEventStore/rails_event_store,mlomnicki/rails_event_store,arkency/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,mlomnicki/rails_event_store