In commit 9b37e7d0, the logic of
`streak_celebration_is_active` was accidentally
changed such that it no longer checks the
Progress Milestones waffle flag.
This commit fixes that.
Note: This also adds in a transitive check to
`courseware_mfe_is_active`,
which makes sense for Streak Celebration
and should not have any functional impact.
05dbd83290