Move Statistics out of the sysimage

[nalimilan]

And remove uses of it in the manual and tests.

Follow-up from #44247. Should probably run PkgEval if the PR looks OK.

I'd suggest trying this, and only move mean and/or std to Base if people complain too loudly before 1.9 is released. Personally I would rather keep these in Statistics to be group statistics function in a single package at last (merging with StatsBase). This makes sense e.g. because these have methods taking weight vectors that we have considered turning into a keyword argument. Also std relies on var so these cannot really be separated.

[ViralBShah]

The main argument is that mean and std are used commonly by people as general tools and people who are not doing serious statistics. I personally am ok with moving these, since it is easier to install packages than ever before.

[nalimilan]

@nanosoldier runtests(ALL, vs = ":master")

[ViralBShah]

This is just moving out of the sysimage, so should be practically risk free.

[nanosoldier]

Your package evaluation job has completed - possible new issues were detected. A full report can be found here.

[nalimilan]

I don't see anything suspicious in the 23 new package test failures reported by Nanosoldier.

[ViralBShah]

We should merge once @KristofferC gives a green light.

[KristofferC]

I think this should be fine. Fully moving it out requires a little bit of thinking about how to deal with compat but I have a strategy that I think should work.