Revert "Trigger labsync generator when upload is done"

This reverts commit d443e880d5.

While the pipeline is still running, labsync generator can't retrieve
its result as it is not yet marked as successfully finished.

Therefore, it is easier to use a webhook instead

builder/Dockerfile

@@ -5,7 +5,6 @@ RUN apk add --no-cache \
 		aws-cli \
 		ca-certificates \
 		coreutils \
-		curl \
 		libffi \
 		mktorrent \
 		openssh-client \