Deprecated C++ std methods

[bertcarnell]

From CRAN:

Dear maintainer,

Please see the problems shown on
https://cran.r-project.org/web/checks/check_results_lhs.html.

Specifically, please see the installation warnings for
r-devel-linux-x86_64-debian-gcc: these can be reproduced by using a
current snapshot of the GCC 12 toolchain.

GCC 12 adds new warnings for use of C++ standard library features that
are deprecated (or no longer present at all) in recent C++ standards,
including std::unary_function and std::binary_function.

See "C++ Standard Library deprecations" in
https://gcc.gnu.org/gcc-12/porting_to.html for more information.

Can you please fix as necessary?

Please correct before 2022-03-29 to safely retain your package on CRAN.

Best,
-k

[bertcarnell]

Fixed with d23832f