cleanup(webhooks): remove delegation webhook trigger support

[romitg2]

What this does

• removes DELEGATION_CREDENTIAL_ERROR from the supported webhook trigger list
• removes the remaining webhook notification test that still treated delegation webhook delivery as active support
• keeps the existing no-op delegation webhook helper in place so unrelated app-store callers keep compiling until broader delegation cleanup lands

Validation

yarn vitest run packages/features/webhooks/lib/service/WebhookNotificationHandler.test.ts

Result: passed (11 tests)

yarn type-check:ci --force

Result: passed

[github-actions]

Hey there and thank you for opening this pull request! 👋🏼

We require pull request titles to follow the Conventional Commits specification and it looks like your proposed title needs to be adjusted.

Details:

Unknown release type "cleanup" found in pull request title "cleanup(webhooks): remove delegation webhook trigger support". 

Available types:
 - feat: A new feature
 - fix: A bug fix
 - docs: Documentation only changes
 - style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
 - refactor: A code change that neither fixes a bug nor adds a feature
 - perf: A code change that improves performance
 - test: Adding missing tests or correcting existing tests
 - build: Changes that affect the build system or external dependencies (example scopes: gulp, broccoli, npm)
 - ci: Changes to our CI configuration files and scripts (example scopes: Travis, Circle, BrowserStack, SauceLabs)
 - chore: Other changes that don't modify src or test files
 - revert: Reverts a previous commit

[github-actions]

This PR has been marked as stale due to inactivity. If you're still working on it or need any help, please let us know or update the PR to keep it active.