Removed event_id from fixture & updated tests

Event_id was used in some of the stacktach smoke tests,
but it was very cumbersome to keep updating the event_id every
month as the data gets purged after 30 days. Hence, removing it
from here & updated tests with event_id which is getting fetched
from an event name

Change-Id: Ie58628b1a2634417c490b42bd9c157d42fb2ded3