w32: Fix closing for non-socket HANDLE.

* src/system-w32.c (__assuan_close): Revert the change.

There are use cases where closing output_fd / input_fd which
may be not socket.

• Fixes-commit: c93eb901e58d5b31294c2d452659b5150d95ec59
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>