operations: Structured errors in UserCreateBranch
With 2e642ccd (branches: Use 'UserCreateBranchError' behind a flag) we
have started using structured errors for the UserCreateBranch RPC
instead of relying on Internal
errors.
This code was rolled out to production and the feature flag is currently enabled by default. Let's remove the feature flag guarding it.
Changelog: changed
Closes #4455 (closed)