on nixpkgs versions prior to the commit that changed
config.system.build's type from a lazy attribute set to a submodule.
Prior to this type change, there is no system.build.kexec_tarball option
declared, so the NixOS module system does not resolve
priorities/overrides in the config.build.kexec_tarball definition.
That is, with lib.mkForce, the config.build.kexec_tarball definition
ends up being something like:
{
_type = "override";
content = <...>;
priority = 50;
}
Removing lib.mkForce allows us to successfully and sensibly interpolate
the value (== outPath) of system.build.kexec_tarball in
system.build.kexec_bundle's builder script.
Likewise, no lib.mkOverride for system.build.raw.
