Remove workaround for https://github.com/fsharp/fsharp/issues/190 in numerics tests.

The Mono bug this is working around was fixed in late 2013, and is in the Mono 3.2 series
that F# already strongly recommends.
Merge pull request #323 from RAOF/remove-obsolete-unit-test-workaround

Remove workaround for https://github.com/fsharp/fsharp/issues/190 in numerics tests