In commit e903a9fc (Utilities/Release: Create a Windows 64-bit binary,
2016-03-16, v3.6.0-rc1~235^2~2) we added a `_USING_V110_SDK71_` macro to
tell the MSVC standard library headers they were using an older SDK.
The environment in which our Windows binaries are produced has been
updated to use a Windows 10 SDK now that we do not need to support
WinXP, so we can drop the definition.