build: remove cache for final image

Remove the `--cache-from` that sources the latest nextstrain/base image
from docker.io. This will force all steps of the final image to re-run
but that should be minimal since it's mostly copying directories
from the builder image.

devel/build

@@ -75,8 +75,6 @@ docker buildx build \
     --build-arg GIT_REVISION \
     --cache-from "$BUILDER_IMAGE:latest" \
     --cache-from "$BUILDER_IMAGE:$tag" \
-    --cache-from "$FINAL_IMAGE:latest" \
-    --cache-from "$FINAL_IMAGE:$tag" \
     --cache-from "$registry/$BUILDER_IMAGE:latest" \
     --cache-from "$registry/$BUILDER_IMAGE:$tag" \
     --cache-from "$registry/$FINAL_IMAGE:latest" \