Removed grub-pc from anon-shared-packages-dependencies. This is a weird dependency. The grub-pc should be already get installed in build-steps.d/1300_create-raw-image build step by grml-debootstrap (./grml_packages) which is fine for VM builds. For --install-to-root users it's unnecessary, since they already have a booting system. As per https://github.com/Whonix/Whonix/issues/342.