ref(flags): Remove organizations:performance-transaction-name-only-search

[wedamija]

Dev-only flag registered Jan 2023, never rolled out to customers. Remove the flag registration and the unreleased gated code paths.

[github-actions]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[github-actions]

📊 Type Coverage Diff

✅ No new type safety issues introduced. Coverage: 93.56%

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit acf3d5c. Configure here.}