Remove `version` parameter/column from Feature Flags API/table

Proposal

In #254324 (closed), we removed access to Legacy Feature Flags for customers. To complete the removal, after becoming confident letting the Feature Flag block access to the Legacy Feature Flag, we will clean up the old feature flag code in our code base.

This should be done after we clean up the Legacy Feature Flag data in #333459 (closed)

Technical proposal

• clean up all references to the feature flag verison column
  • lib/api/feature_flags.rb
  • app/models/operations/feature_flag.rb
  • app/finders/feature_flags_finder.rb
  • app/assets/javascripts/feature_flags/constants.js
  • app/assets/javascripts/feature_flags/store/edit/mutations.js
  • app/assets/javascripts/feature_flags/store/edit/state.js
• drop feature flags version column