unit: enqueue cgroup empty check event if the last ref on a unit is dropped
(cherry picked from commit e5c36295d81971ef75d9c6f98f0890b92a4a353f)
Resolves: #1697893
patch_name: 0116-unit-enqueue-cgroup-empty-check-event-if-the-last-re.patch
present_in_specfile: true
location_in_specfile: 116
squash_commits: true