Remove the Visual Studio 2013 toolchain references #249

Upstream: HaxeFoundation/hxcpp#1428 by @tobil4sk (open PR).

Visual Studio 2013 can't build hxcpp: it lacks full C++11 (char16_t, constexpr), so include/hx/LessThanEq.h already fails to compile with it. The toolchain still looks for it: toolchain/msvc-setup.bat and toolchain/msvc64-setup.bat fall back to %VS120COMNTOOLS%, and the upstream PR also removes vs2013 handling from toolchain/msvc-toolchain.xml, finish-setup.xml, tools/hxcpp/BuildTool.hx, GenMsvc.hx, Linker.hx, Setup.hx, hxcpp/Builder.hx and docs/build_xml/Compiler.md.

Removing it drops the last msvcrt-producing versions. Keep the -19 object-file suffix for now: Lime relies on it, as the PR notes, so changing it is a breaking change for a later major version.