Use mkinitcpio to create the unified UEFI kernel image instead performing the steps manually via objcopy. There are a couple benefits to this,

1. systemd has documented that the section offsets in the stub will no longer be fixed going forward, so we need to stop hardcoding these and it's best to just let existing tooling discover the offsets.
2. This greatly simplifies the build: no longer are some temporary build files left laying around the working directory. The build.sh script just outputs disk.raw and nothing else.