random: remove call to RAND_screen() (Windows only)

Summary:

Follow up to https://github.com/bitcoin/bitcoin/pull/17151 where
there were multiple calls to also remove our call to RAND_screen().

Backport of core PR17191.

Test Plan: Run the build-win64 CI build plan.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6157