build: remove mingw linker workaround from win gitian descriptor
build: remove mingw linker workaround from win gitian descriptor

Summary:
> This workaround was added as part of the switch to gitian building using Ubuntu 14.04 (#6900).
> However, it should no longer be required, as we have switched to Bionic (#13171), and that
> has a far newer version of binutils.
>
> binutils patch: https://sourceware.org/bugzilla/show_bug.cgi?id=16192

Bitcoin ABC now uses Debian Buster, which has an even more recent version of binutils (2.31 vs 2.30).

This is a backport of [[https://github.com/bitcoin/bitcoin/pull/16667 | core#16667]]

Depends on D10584

Test Plan: @bot gitian-win

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10587

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