Build against local versions of lager and syslog.  Notably, lager has changed
the definition of ?DEBUG etc recently, so if we compile against latest but
use our version then it doesn't work at all.
Revert "Build against local versions of lager and syslog.  Notably, lager has changed"

This reverts commit ef9731e58a50619462513684cb294cf3cac793bf.

We have pulled lager to upstream master recently, so we shouldn't need this patch now.