ZOOKEEPER-3896: Remove badly behaving PollSCM trigger

PollSCM trigger triggers a build every time it scans the ZooKeeper repo regardless the branch pointer has been changed or not. Instead, I try to use the built-in 'Scan Multibranch Pipeline' instead which should be good for the same purpose.

Author: Andor Molnar <andor@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>

Closes #1415 from anmolnar/ZOOKEEPER-3896

Jenkinsfile

@@ -25,7 +25,6 @@ pipeline {
     }
 
     triggers {
-        pollSCM('@hourly')
         cron('@daily')
     }