`Not` exported but not defined

[thorek1]

I am reexporting functions from AxisKeys.jl and Aqua.jl noticed that Not is exported but not defined. It would be nice to resolve this one way or another. In the meantime I will import individual functions so that my tests don't break.

[mcabbott]

This used to be imported from https://github.com/JuliaData/InvertedIndices.jl in order to be exported... that got moved to https://github.com/mcabbott/AxisKeys.jl/blob/master/ext/InvertedIndicesExt.jl but perhaps it should move back.

[thorek1]

that would be one way. I have no preference in that regard