guix: remove gcc-toolchain static from Windows build
Summary:
These do not need to be propogated into the Windows build environment.
Backport of core core#29828
Depends on D17234.
Test Plan: Run the windows GUIX build
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D17235