ci: remove reliance on qemu for building native gems

note that we still need qemu for testing the installed
binaries. (aarch64 absolutely, but we could get away without doing it
on 32-bit x86 if we wanted.)

.github/workflows/precompiled.yml

@@ -77,7 +77,6 @@ jobs:
           path: precompiled/ports/archives
           key: archives-ubuntu-${{hashFiles('precompiled/ext/precompiled/extconf.rb')}}
       - run: |
-          docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
           docker run --rm -v "$(pwd)/precompiled:/precompiled" -w /precompiled \
             larskanis/rake-compiler-dock-mri-${{matrix.plat}}:1.2.0 \
             ./bin/test-gem-build gems ${{matrix.plat}}