Remove this errant test::unit test

This test requires a bunch of static data and as far as I know, nobody has run it for years. The only Test::Unit stuff we should see in Metasploit these days are the ones in our local forks of old Ruby libraries.

## Verification

- [x] No Metasploit-native libs should be shipping with unit tests any more. Run: `grep -ril 'test/unit' lib` and see results like so:

````
lib/metasm/tests/expression.rb
lib/metasm/tests/ia32.rb
lib/metasm/tests/parse_c.rb
lib/metasm/tests/arc.rb
lib/metasm/tests/preprocessor.rb
lib/metasm/tests/dynldr.rb
lib/metasm/tests/encodeddata.rb
lib/metasm/tests/x86_64.rb
lib/metasm/tests/mips.rb
lib/metasm/tests/dasm.rb
lib/net/ssh/test.rb
lib/zip/test/stdrubyexttest.rb
lib/zip/test/ziptest.rb
lib/zip/test/zipfilesystemtest.rb
lib/zip/test/ioextrastest.rb
lib/zip/test/ziprequiretest.rb
````