Remove `ci_skip_before_parsing_yaml` feature flag
What does this MR do?
Removes code for the ci_skip_before_parsing_yaml
feature flag, including the now obsolete LegacySkip
class. This feature flag has previously be defaulted to true in %14.2: !67839 (merged)
Issue
Feature flag rollout: #337167 (closed)
Feature issue: #235855 (closed)
Edited by Avielle Wolfe