Migrate features_usage_data_ce from usage_data.rb

As a part of the effort to remove usage_data.rb file we can now remove features_usage_data_ce method.

It contains 14 metrics. All are straightforward (for example Gitlab.config.registry.enabled - system setting).

As the outcome we need to have:

1. the subject method and associated specs to be removed
2. instrumentation classes with specs created for all 14 metrics
3. metrics definition updated to enable usage of the classes