I wanted to do the same thing, so I went on an adventure.
Somewhere along the line, the thing that stores failed jobs to the DB is registered (QueueServiceProvider->registerFailedJobServices)
This has the nice, probably-undocumented ternary statement:
if a queue.failed table is set, send failed jobs to the db. Otherwise, just ignore them (QueueServiceProvider line 199, as of Feb 5 2018)
So, to disable this functionality, and avoid the errors in your log file, set 'failed.table' to null in your config/queue.php. (By default, it's set to failed_jobs).