Updated spec based on feedback

to ensure that the spec fails in case the participant.events
do not exist.
Added @fixed #2374

for the commit that was examined for the reason
of Date.today/Time.now existing
Merge branch 'master' of https://github.com/NUBIC/ncs_navigator_core
Removed unused spec

NCSNavigator::Core::JSONValidator was removed
so no need to test it