RFC: Remove deprecated primes and combinatorics functions from Base

[ararslan]

These functions were present in 0.4, are deprecated in 0.5 in favor of JuliaMath packages, and—if I understand the deprecation cycle correctly—should now be removed in 0.6. If that's not the case, we can close the PR or let it stagnate until they're ready to be removed.

Having isdefined(Base, :isprime) == true (and likewise for other functions) is messing with the documentation for Primes.jl generated by Documenter; it calls them Base.isprime, etc. So it would be nice from that perspective if that were now false.

[ararslan]

The 32-bit Windows failure is both unrelated and strange.

Edit: It's probably #16555

Edit 2: Restarting AppVeyor seems to have done the trick. 🎉

[tkelman]

This is a little earlier than we usually remove deprecations, but I guess if it's causing problems then ok. Won't you need a solution to the Documenter issue with Primes.jl on 0.5?

[ararslan]

This is a little earlier than we usually remove deprecations

Okay, feel free to close or just let the PR stagnate, then when it's ready to be removed I can reopen or rebase as necessary. I'm fine with whatever. 👍

Won't you need a solution to the Documenter issue with Primes.jl on 0.5?

Yep. So far my solution is "hope users aren't confused by the docs listing the functions with the Base prefix." I'm at a loss for something better.

[ararslan]

The macOS failure is unrelated (some linker failure)

[tkelman]

travis can be finicky about when changes to the yml file take effect, here for the llvm version switch - this passed CI a few months ago, going to just squash merge