More java.text test cleanup/fixes.

I investigated http://bugs.icu-project.org/trac/ticket/10353 further
and decided it's WAI, so we can remove a TODO implying that icu4c was
incorrect. Also merge the remaining OldDecimalFormatTest tests, removing
duplication.

Change-Id: I1941dd1bef3b5eae258960ca8a5fcd2e7de0c926