Remove unused feature flag to fix broken master

Master pipelines fail because there is an unused feature flag

config/feature_flags/development/usage_data_design_action.yml

----
-name: usage_data_design_action
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/46626
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/287630
-milestone: '13.7'
-type: development
-group: group::knowledge
-default_enabled: true