event.rb

Per GitLab.com's performance metrics this method could take up to 5
seconds of wall time to complete, while only taking 1-2 milliseconds of
CPU time. Removing the Redis lease in favour of conditional updates
allows us to work around this.

A slight drawback is that this allows for multiple threads/processes to
try and update the same row. However, only a single thread/process will
ever win since the UPDATE query uses a WHERE condition to only update
rows that were not updated in the last hour.

Fixes gitlab-org/gitlab-ce#22473