Auto merge of #114080 - compiler-errors:negative, r=spastorino

Don't treat negative trait predicates as always knowable

We don't need this. It was added in #90104 but I don't really know why. It's not sound afaict -- negative trait predicates need the same coherence-ambiguity/orphan check rules as positive ones.

r? `@lcnr`

cc `@spastorino,` do you remember why?

Author: bors