Fix Ruby not starting if newer version of date gem installed

What does this MR do and why?

If you had date v3.3.4 installed, Puma and Sidekiq would not start due to this error message:

`check_for_activated_spec!': You have already activated date 3.3.4, but your Gemfile requires date 3.3.3. Prepending `bundle exec` to your command may solve this. (Gem::LoadError)

This occurred because the require 'date' inside vendor/gems/attr_encrypted/attr_encrypted.gemspec caused Ruby to load the latest version of date, but then this conflicts with the version specified in Gemfile.lock. More details in https://github.com/rubygems/rubygems/issues/7178#issuecomment-1821963836.

To avoid this problem, drop the use of the date in the gemspec.

How to set up and validate locally

1. Run gem install date.
2. Run bundle exec irb.

Without this change, you hit this failure.