Delete `resign_kernel_partition.sh`

This script is no longer used iiuc.

BUG=none
TEST=builders/release/CQ

Change-Id: I967d4fcae8392a54f2562a19a43a706a039db355
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/6838147
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Jae Hoon Kim <kimjae@chromium.org>