R1:fbfed82efdde

Add a missing DaemonLogEvent key for garbage collection

Summary: See PHI176. This is issued periodically by the garbage collector. Normally this table is relatively small-ish so this missing key isn't hugely noticeable.

Test Plan:
Ran `./bin/garbage collect --collector daemon.processes --trace` to get the query the GC runs.

Ran ##DELETE FROM `daemon_logevent` WHERE epoch < 1508443504 LIMIT 100## before and after the key, saw a much better query plan afterward:

Before:

```
mysql> explain DELETE FROM…