dev-haskell/vector: drop USE=test, bug #666812

dev-haskell/vector: drop USE=test, bug #666812

Test suite is not compatible with modern QuickCheck instances:

```
tests/Utilities.hs:54:10: error:
    Duplicate instance declarations:
      instance Arbitrary a => Arbitrary (Identity a)
        -- Defined at tests/Utilities.hs:54:10
        -- Defined in ‘Test.QuickCheck.Arbitrary’
```

Let's drop test suite and fix it in text vector release.

Reported-by: Pacho Ramos
Closes: https://bugs.gentoo.org/666812
Package-Manager: Portage-2.3.49, Repoman-2.3.11