Clean up dependency_list_ui feature flag and old code paths

#195928 (closed) changes the Dependency List UI. Those changes are implemented behind the dependency_list_ui feature flag.

Once #195928 (closed) has been completed, the feature flag and old code paths/components should be cleaned up.

This includes (but is not limited to):

• Removing completely
  • ee/app/assets/javascripts/dependencies/components/dependencies_table_row.vue and tests
• Deleting old code paths where the feature flag is disabled
  • ee/app/assets/javascripts/dependencies/components/app.vue
  • ee/app/assets/javascripts/dependencies/components/dependencies_table.vue
• Refactoring the Vuex store, to remove some complexity introduced by having two tabs in the previous UI.