hikey: Remove 3.18 kernel prebuilts

Support for 3.18 has been dropped.

Change-Id: I13849fb95994eb0132738adbf968189bc277b983
Signed-off-by: Alistair Strachan <astrachan@google.com>
diff --git a/Image.gz-dtb-3.18 b/Image.gz-dtb-3.18
deleted file mode 100644
index 3a54d43..0000000
--- a/Image.gz-dtb-3.18
+++ /dev/null
Binary files differ
diff --git a/hi6220-hikey.dtb-3.18 b/hi6220-hikey.dtb-3.18
deleted file mode 100644
index 688cbf1..0000000
--- a/hi6220-hikey.dtb-3.18
+++ /dev/null
Binary files differ