kdump-lib.sh: Remove is_atomic

Now all atomic special workaround is removed, we can remove the atomic
detection function.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

kdump-lib.sh

@@ -321,11 +321,6 @@ kdump_get_persistent_dev() {
     echo $(get_persistent_dev "$dev")
 }
 
-is_atomic()
-{
-    grep -q "ostree" /proc/cmdline
-}
-
 is_ipv6_address()
 {
     echo $1 | grep -q ":"