Remove Slack notifications feature flag
What does this MR do?
Remove Slack notifications feature flag
Slack notifications sent from release-tools have been used for the past
month, as such, I believe we can deem them stable. This commit removes
the feature flag from the CoordinatedPipeline::Notifier
class and the
specs.
Related to gitlab-com/gl-infra/delivery#2071 (closed)
Author Check-list
- [-] Has documentation been updated?
Edited by Mayra Cabrera