ticket:8464: Apply Markus' changes. _COUNT -> _UNIT_COUNT.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@34684 251d0590-4201-4cf1-90de-194747b24ca1
ticket:8464: Merge r34629 to r34684 from trunk.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@34685 251d0590-4201-4cf1-90de-194747b24ca1