anaconda: Do not rely on new-kernel-pkg

Qubes OS does not use grubby, so there is no need to check for the
existence of the new-kernel-pkg executable.

anaconda/pyanaconda/packaging/__init__.py

@@ -531,10 +531,6 @@ class Payload(object):
 
             :returns: None
         """
-        if not os.path.exists(iutil.getSysroot() + "/usr/sbin/new-kernel-pkg"):
-            log.error("new-kernel-pkg does not exist - grubby wasn't installed?  skipping")
-            return
-
         for kernel in self.kernelVersionList:
             log.info("recreating initrd for %s", kernel)
             if not flags.imageInstall: