[libFuzzer][Windows] Clean up RawPrint

Summary:
Use `_write` instead of the deprecated alias `write` on Windows.
Also, remove comment saying RawPrint is untested on Windows.

Reviewers: vitalybuka

Reviewed By: vitalybuka

Subscribers: vitalybuka

Differential Revision: https://reviews.llvm.org/D57589

llvm-svn: 353108