Remove obsolete CXX_STD = CXX11 to allow Armadillo 15.0.x migration

[eddelbuettel]

Armadillo 15.0.* now makes C++14 the minimum compilation standard. For most packages, adapting to it can be very simple, and yours is one of them. In this PR we simply remove the declaration from Makevars and Makevars.win -- and no other changes are needed.

Please see issues #475 and below for context, and notably #489 for this first wave of PRs. It would be terrific if you could make an upload to CRAN 'soon' to remove the reliance on C++11 which we needed in the past, but which is by now a hindrance. Of course, CRAN also now wants you to remove C++11 use and imposed a deadline on your package. Using the PR and re-uploading will help you meet this.

Please do not hesitate to reach out if I can assist in any way or clarify matters.

[eddelbuettel]

I noticed you updated you main branch so I rebased the PR to remain its one small commit ahead of your updated state.

[shwilks]

Wow thanks a lot for taking the time to do the above! I'll submit an updated package version to CRAN now

[eddelbuettel]

It was one of those things -- I noticed a message from GitHub in the stream of messages (filtered away to another folder) without an actual GitHub notification so I was for a second confused. It was simply from the initial CI run when you had allowed it for the PR so then I noticed that your main branch was much updated relative to the one I had started from (as your 'pending' work was all in a branch...) All good, and lucky chance I caught it.

Thanks for merging, and for an update at CRAN -- much appreciated.

[shwilks]

aha, yes there were some changes that included a more detailed snapshot test, so I figured that was probably worth merging in first. Thanks again for reaching out, the new version is on its way to CRAN now so hopefully should be a straightforward update soon!