Revert "Block new-user INSERT during organization read-only mode"

Abdul Wadoodrequested to merge
604050-revert-block-new-user-insert into master

What does this MR do and why?

Reverts !242419 (merged), which blocked new-user INSERTs (SSO auto-creation) while an organization is in read-only mode.

This enforcement is no longer needed: there won't be auth exemptions during organization read-only mode, per gitlab-com/content-sites/handbook!20741 (merged).

References

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