Drop project_id not null constraint ci_deleted_objects

What does this MR do and why?

Ref: #495123 (closed)

Following up !168024 (merged) where we fixed this bug in %17.5 we are now backporting it to %17.4.

This commit drops check_98f90d6c53 constraint to unblock the accumulation of ci_job_artifacts that needs to be clean up from the system.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

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