Revert "arm64: port MR!1692 ("Test suite: configure UEFI boot...")"

This reverts commit 7a2bade6.

For some reason Debian testing's qemu+libvirt+edk2+grub(unsigned)
stopped working with secure-boot enabled, revert the commit that
re-enabled it (it's unsupported anyway on asahi) to run the test
suite.