Revert "Clarify `eqv` with zero-denominator Rationals"
Revert "Clarify `eqv` with zero-denominator Rationals"

This reverts commit ef2a93b9819ae2d2a520c561111a5718eded83ca.

Bugginess with zero-denomitor Rationals math got discovered[^1] and
when it's fixed, it's possible there won't even be any
zero-denominator Rationals that have numerators other than <1 -1 0>

[1] https://irclog.perlgeek.de/perl6-dev/2017-12-31#i_15635846

antquinonez/doc,perl6/doc,MasterDuke17/doc,perl6/doc,tbrowder/doc,jonathanstowe/doc,MasterDuke17/doc,perl6/doc,gfldex/doc,perl6/doc,gfldex/doc,stmuk/doc,jonathanstowe/doc,dmaestro/doc,dmaestro/doc,gfldex/doc,MasterDuke17/doc,jonathanstowe/doc,MasterDuke17/doc,antquinonez/doc,stmuk/doc,stmuk/doc,gfldex/doc,stmuk/doc,tbrowder/doc,tbrowder/doc,jonathanstowe/doc,jonathanstowe/doc,dmaestro/doc,stmuk/doc,antquinonez/doc,tbrowder/doc,perl6/doc,gfldex/doc,antquinonez/doc,dmaestro/doc,antquinonez/doc,dmaestro/doc