Try deleting the one(::Any) and zero(::Any) non_diff methods

[MasonProtter]

Attempt at alternative to JuliaDiff/ChainRulesCore.jl#653 for fixing #769

[oxinabox]

Yes, this seems to fix the problem in Diffractor and these methods are kinda wrong anyway,
since we do need to have a zero value here, the tanget space does (in general) exist.
This matters for forward mutation support in Diffractor where NoTangent() gets left as is, but ZeroTangent gets made into a a concrete zero value if it is mutable.

(zeros is also wrong, I'll make another PR for that)

Fixes #769

[oxinabox]

Remaining CI issues are unrelated so merging