Remove unused INITRD variable

Change-Id: I18777b815ca119dc8451e2378356a0f264717e9b
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/classes/image-overlay.bbclass b/classes/image-overlay.bbclass
index 68acca9..f0c4060 100644
--- a/classes/image-overlay.bbclass
+++ b/classes/image-overlay.bbclass
@@ -2,7 +2,6 @@
 EXCLUDE_FROM_WORLD = "1"
 
 INITRD_IMAGE ?= "obmc-phosphor-initramfs"
-INITRD ?= "${DEPLOY_DIR_IMAGE}/${INITRD_IMAGE}-${MACHINE}.cpio.${INITRD_CTYPE}${uboot}"
 
 IMAGE_BASETYPE ?= "squashfs-xz"
 OVERLAY_BASETYPE ?= "jffs2"