cmp_deeply dies when using only Test::Deep::NoTest

```pl
use Test::Deep::NoTest;
my $res = cmp_deeply([1,2,3], [4,5,6]);
```

    Can't call method "ok" on an undefined value at .../Test/Deep.pm line 204.

Line 204 is doing `if (not $Test->ok($ok, $name))`, but `$Test` is not defined because this is `NoTest`.