Fix SetHash internal `proxy` sub from treating negatives as positive
Fix SetHash internal `proxy` sub from treating negatives as positive

Adjusts behaviour to follow commit message in previous[^1] commit about
giving SetHash same semantics as Bag/MixHashes; such as:
`$_ = -1 for $sethash.values` deleting elements instead of leaving them in.

[1] https://github.com/rakudo/rakudo/commit/e5b5d3461d300fe4ae36d3a1f1909613c222ab26

tony-o/rakudo,salortiz/rakudo,raydiak/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tony-o/rakudo,Gnouc/rakudo,sjn/rakudo,jonathanstowe/rakudo,sjn/rakudo,raydiak/rakudo,MasterDuke17/rakudo,rakudo/rakudo,softmoth/rakudo,tony-o/rakudo,salortiz/rakudo,labster/rakudo,nbrown/rakudo,nbrown/rakudo,labster/rakudo,tbrowder/rakudo,tbrowder/rakudo,awwaiid/rakudo,labster/rakudo,lucasbuchala/rakudo,softmoth/rakudo,tony-o/rakudo,rakudo/rakudo,sjn/rakudo,usev6/rakudo,labster/rakudo,softmoth/rakudo,nbrown/rakudo,salortiz/rakudo,usev6/rakudo,usev6/rakudo,Gnouc/rakudo,awwaiid/rakudo,tony-o/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,rakudo/rakudo,awwaiid/rakudo,raydiak/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,salortiz/rakudo,MasterDuke17/rakudo,salortiz/rakudo,softmoth/rakudo,sjn/rakudo,awwaiid/rakudo,tbrowder/rakudo,rakudo/rakudo,sjn/rakudo,usev6/rakudo,raydiak/rakudo,usev6/rakudo,tbrowder/rakudo,lucasbuchala/rakudo,labster/rakudo,Gnouc/rakudo,labster/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,salortiz/rakudo,tony-o/rakudo,awwaiid/rakudo,rakudo/rakudo,nbrown/rakudo,nbrown/rakudo,softmoth/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,Gnouc/rakudo,nbrown/rakudo,jonathanstowe/rakudo