Remove hanging ';' in some os attributes

Some os attributes (2) have a "hanging" semi-colon, probably where
another os value has previously been removed but not the associated
divider.

I've removed these as a prelude to an additional check I wish
to add to tools/test.py to pick up unknown os values.

Change-Id: I469ea81f5a48f762cd0f6f2e92d457416360976e
backport: havana