localhost-to-dockerhub: Remove inapplicable RepoDigests check

Checking RepoDigests is only possible if the images are retained in the
local Docker host (different from the local registry).
That is not the case anymore with buildx build --push.

An equivalent error should arise from copy-image() if the image is not
first pushed to the local registry.

devel/localhost-to-dockerhub

@@ -5,8 +5,6 @@
 # This pushes just the provided tag. If "latest" is provided as a second argument,
 # the provided tag will also be pushed as "latest"
 #
-# Errors if any of the tagged images have already been pushed.
-#
 set -euo pipefail
 
 if [[ $# -lt 1 ]]; then
@@ -19,11 +17,6 @@ tag=$1
 BASE_IMAGE="nextstrain/base"
 BASE_BUILDER_IMAGE="nextstrain/base-builder"
 
-if [[ $(docker image inspect --format "{{.RepoDigests}}" $BASE_IMAGE:$tag) != '[]' || $(docker image inspect --format "{{.RepoDigests}}" $BASE_BUILDER_IMAGE:$tag) != '[]' ]]; then
-    echo "At least one of $BASE_IMAGE:$tag and $BASE_BUILDER_IMAGE:$tag has already been pushed. This can happen if the newly built image is not available in the local registry." >&2
-    exit 1
-fi
-
 
 # Use Skopeo via a Docker container to copy a tagged image.
 # https://github.com/containers/skopeo/blob/07da29fd371dd88615a0b86e91c6824237484172/install.md#container-images