bpo-37758: Clean out vestigial script-bits from test_unicodedata. (GH-15126)

bpo-37758: Clean out vestigial script-bits from test_unicodedata. (GH-15126)

This file started life as a script, before conversion to a
`unittest` test file.  Clear out some legacies of that conversion
that are a bit confusing about how it works.

Most notably, it's unlikely there's still a good reason to try
to recover from `unicodedata` failing to import -- as there was
when that logic was first added, when the module was very new.
So take that out entirely.  Keep `self.db` working, though, to
avoid a noisy diff.