Use variadic templates unconditionally

[eddelbuettel]

As described in #1366 and building on PR #1364, we can simplify the code by no longer switching based on definition of HAS_VARIADIC_TEMPLATE: only the positive case will be considered given the baseline of C++11.

So this PR removed this file by file, testing each commit locally in CI and arrived at removing the definition. A reverse dependency check is now running as well.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[eddelbuettel]

Don't get to do that every day 😆

[kevinushey]

Don't get to do that every day 😆

It's beautiful!

[eddelbuettel]

I was a little surprised it amounted to so little in the tar.gz:

edd@rob:~/git/rcpp(feature/variadic_templates)$ ls -tltr Rcpp_1.0.14.[78].tar.gz -rw-r--r-- 1 edd edd 2972038 Mar 16 09:51 Rcpp_1.0.14.7.tar.gz -rw-r--r-- 1 edd edd 2889287 Mar 18 20:37 Rcpp_1.0.14.8.tar.gz edd@rob:~/git/rcpp(feature/variadic_templates)$ 

[kevinushey]

LGTM!

[eddelbuettel]

Been burned before so I will probably await the reverse-depends. Maybe just maybe somone relied on the define. Otherwise this is pretty easy (if volumunious): no new code, only removal of code we no longer compiled in. Seemingly no fat-fingered typo ... 🤞

[Enchufa2]

Nice!