Revert "Reland "Consider winsdk_samples a system library.""

This reverts commit 9c9f3c9268c7d573880ef6eabd55ee12d8c46a1d.

Reason for revert: Using -imsvc warnings are still considered.

Change-Id: Ibe23541c075d8450bb839ed419af7c94cbaecbe7
Reviewed-on: https://webrtc-review.googlesource.com/76522
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>