No cov(::AbstractMatrix, ::Bool) method

[nalimilan]

Currently cov(x, false) fails when x is a matrix rather than a vector: you need to use cov(x, 1, false). This is annoying since 1) the docstring appears to imply the both arguments are optional, and 2) it makes it harder to find the replacement for the deprecated cov(x, corrected=false) method.

Is this just an oversight?

Cf. https://discourse.julialang.org/t/what-is-the-current-best-practice-for-population-formula-for-cov/658

[andreasnoack]

There might be some cleanup left after the removal of the keyword arguments. However, we should think of this with #19451 in mind. We have very few functions left that defaults to dim=1 so we should consider deprecating the cov(Matrix) method.

[nalimilan]

Right. Maybe the best thing to do is improving the deprecation warning.

[nalimilan]

cov now takes a corrected keyword argument.