Remove usage_data_i_snippets_show FF

Remove left over
usage_data_i_snippets_show
feature flag.

Changelog: other

config/feature_flags/development/usage_data_i_snippets_show.yml

----
-name: usage_data_i_snippets_show
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48113
-rollout_issue_url:
-milestone: '13.7'
-type: development
-group: group::editor
-default_enabled: true

lib/gitlab/usage_data_counters/known_events/common.yml

@@ -324,7 +324,6 @@
   category: snippets
   redis_slot: snippets
   aggregation: weekly
-  feature_flag: usage_data_i_snippets_show
 # Terraform
 - name: p_terraform_state_api_unique_users
   category: terraform