hack: remove outdated comment (#1739)

hack/k8s/codegen/Dockerfile

@@ -3,7 +3,5 @@ FROM golang:1.9-alpine
 RUN apk add --update --no-cache git bash \
   && go get -u k8s.io/code-generator || true \
   && cd src/k8s.io/code-generator \
-  # We need to go install here and get rid of go install in the script
-  # due to upstream path assumption causing dependency issues.
   && go install ./cmd/... \
   && sed -i '/go install .\//d' ./generate-groups.sh