chore: remove extraneous dockerfile

hack/dockerfiles/legacy.Dockerfile

@@ -1,47 +0,0 @@
-FROM golang:1.15-alpine AS base
-
-# Create the user and group files that will be used in the running container to
-# run the process as an unprivileged user.
-RUN mkdir /user \
-  && echo 'nobody:x:65534:65534:nobody:/:' >/user/passwd \
-  && echo 'nobody:x:65534:' >/user/group
-
-# Install the Certificate-Authority certificates for the app to be able to make
-# calls to HTTPS endpoints.
-# Git is required for fetching the dependencies.
-RUN apk add --no-cache ca-certificates git
-
-# Set the working directory outside $GOPATH to enable the support for modules.
-WORKDIR /src
-
-# Fetch dependencies first; they are less susceptible to change on every build
-# and will therefore be cached for speeding up the next build
-COPY ./go.mod ./go.sum ./
-RUN go mod download
-
-# Import the code from the context.
-COPY ./ ./
-
-FROM base AS export-to-gcs
-
-RUN CGO_ENABLED=0 go build \
-  -installsuffix "static" \
-  -o /export-to-gcs ./src/legacy/export-to-gcs
-
-# Final stage: the running container.
-FROM scratch AS final
-
-# Import the user and group files from the first stage.
-COPY --from=base /user/group /user/passwd /etc/
-
-# Import the Certificate-Authority certificates for enabling HTTPS.
-COPY --from=base /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
-
-# Import the compiled executable from the first stage.
-COPY --from=export-to-gcs /export-to-gcs /export-to-gcs
-
-# Perform any further action as an unprivileged user.
-USER nobody:nobody
-
-# Run the compiled binary.
-ENTRYPOINT ["/export-to-gcs"]