Remove MetaProgrammingLibrary and replace by C++14 STL equivalents

Since we started requiring C++11 `itk::mpl` is fairly redundant. Even more so now that we require a minimum of C++14. It is desireable to completely remove this and rely on standard template library and language features directly.

Part of this is already accomplished, mostly by #2730, but also in part by d3e151f09d04830c8ef6ac2f2b104d247ffb99f3 and perhaps some other, earlier refactoring.