[v6.d REVIEW] Toss .is-prime tests on unreduced rats
[v6.d REVIEW] Toss .is-prime tests on unreduced rats

It's now a requirement for Rationals to be reduced on creation,
so these tests don't make sense and .is-prime is well-covered already

Orig: https://github.com/perl6/roast/commit/a71839ea2

dogbert17/roast,perl6/roast,dogbert17/roast