Remove inapplicable RepoDigests check

Checking RepoDigests is only possible if the images are retained locally
(not in the local registry). That is not the case anymore with --push.

An equivalent error should arise from the skopeo command 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
-
 # copy local $tag to remote $tag
 skopeo copy --multi-arch=all --src-tls-verify=false docker://localhost:5000/$BASE_IMAGE:$tag docker://docker.io/$BASE_IMAGE:$tag
 skopeo copy --multi-arch=all --src-tls-verify=false docker://localhost:5000/$BASE_BUILDER_IMAGE:$tag docker://docker.io/$BASE_BUILDER_IMAGE:$tag