Cleanup the last Windows / MSC ifdefs and comments

Merged Ondřej Surý requested to merge ondrej/cleanup-windows-bits into main

Cleanup the remnants of MS Compiler bits from <isc/refcount.h>, printing the information in named/main.c, and cleanup some comments about Windows that no longer apply.

The bits in picohttpparser.{h,c} were left out, because it's not our code.

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