Remove combined_project_update_on_event_creation feature flag and code combining queries

Krasimir Angelovrequested to merge
468984-cleanup into master

What does this MR do and why?

Remove combined_project_update_on_event_creation feature flag and the code introduced with it.

See #468831 (comment 2170294849).

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Closes #468984 (closed)

Edited by Krasimir Angelov

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