Partitioning: Drop non-partitioned web_hook_logs table
As the final step of partitioning the `web_hook_logs` table (&5558), we'll remove the non-partitioned archive table.
It will follow the successful swap of the base web_hook_logs table with the partitioned copy (gitlab-org/gitlab#323677), after monitoring for a period of time that it caused no issues. It may be released in the same milestone as gitlab-org/gitlab#323677 are, at worst case scenario, in the milestone that follows it.
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