Remove outdated version of Airbrake hook
Remove outdated version of Airbrake hook

It seems unnecessary to duplicate the code (which is now outdated) in
the README. Instead, link to the built-in hooks where a user can see
the code.

orvice/logrus,brandur/logrus,henrylee2cn/logrus,penhauer-xiao/logrus,lixin9311/logrus,Arkan/logrus,creack/logrus,Sirupsen/logrus,axiomzen/logrus,yxd-hde/logrus,EmileVauge/logrus,dpatel06/logrus,penhauer-xiao/logrus,xyliuke/logrus,seatgeek/logrus,weekface/logrus,Barberrrry/logrus,devopstaku/logrus,pippio/logrus,nicescale/logrus,freeformz/logrus,dradtke/logrus,upstartmobile/logrus,HideoYamauchi/logrus,Dal-Papa/logrus,wallclockbuilder/logrus,torfuzx/logrus,therealbill/logrus,hvnsweeting/logrus,sirupsen/logrus,sirupsen/logrus,alecha/logrus,noxiouz/logrus,derekdowling/logrus,ConnectedHomes/logrus,zbindenren/logrus,yawn/logrus,marcosnils/logrus,cgag/logrus,noironetworks/logrus,akutz/logrus,ineiti/logrus,snowsnail/logrus,ryanfaerman/logrus,gogap/logrus,w4ngyi/logrus,chendrak/logrus,tianon/debian-golang-logrus,TheQuestionru/logrus