OAK-1176: ObservationTest#observationDispose fails every now and then
Reverting some changes from rev. 1541935 as these where very likely made accidentally (left over from reviewing an earlier patch).

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1545636 13f79535-47bb-0310-9956-ffa450edef68