Boost.Contract no longer builds with C++03

[mclow]

it includes any.h, which no longer supports C++03.

Discovered in Boost 1.84.0 Beta 1 Release Candidate 1

[jeking3]

There are also tests that explicitly set BOOST_NO_CXX11_VARIADIC_TEMPLATES to test C++03 compatibility instead of just forcing that test to run if cxxstd=03. I found that both chrono and optional now fail under C++03. I will probably just be removing the C++03 stuff; if someone tries to use it, one of the dependencies will tell them it's not supported.