fetch-vendor-package.sh: Remove the older vendor-package am: 815210a13a

Original change: https://android-review.googlesource.com/c/device/linaro/hikey/+/2146079

Change-Id: Idb7e0f57c9a4df0caee818197c41396908380ba6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>