Removes a redundant user_id field from the pipeline chain validate logs

What does this MR do and why?

Removes a redundant user_id field from the pipeline chain validate logs - this user_id field is redundant given the meta.gl_user_id value is also being emitted via the context.

This MR therefore reduces the complexity of this code marginally, and reduces the load on our logging infrastructure.

References

gitlab-org/quality/quality-engineering/team-tasks#3922

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