remove unused `throughput_stress` folder (#261) #1706

Job	Run time
build-cli	2m 4s
test-kitchensink (go)	2m 7s
test-kitchensink (java)	4m 21s
build-ks-gen-and-ensure-protos-up-to-date	1m 29s
test-kitchensink (typescript)	2m 45s
test-kitchensink (dotnet)	2m 15s
test-kitchensink (python)	2m 5s
prepare-for-docker-push	6s
test-omes	1m 51s
check-worker (typescript)	1m 57s
check-worker (java)	1m 51s
check-worker (go)	57s
build-worker (python)	2m 0s
build-worker (dotnet)	2m 20s
build-worker (typescript)	2m 44s
check-worker (dotnet)	1m 37s
build-worker (java)	2m 37s
build-worker (go)	1m 36s
check-worker (python)	1m 3s
push-docker-images / build-go-docker-images / Publish go to Docker Hub	10m 10s
push-docker-images / build-python-docker-images / Publish python to Docker Hub	11m 16s
push-docker-images / build-dotnet-docker-images / Publish dotnet to Docker Hub	13m 16s
push-docker-images / build-java-docker-images / Publish java to Docker Hub	18m 30s
push-docker-images / build-typescript-docker-images / Publish typescript to Docker Hub	15m 59s
push-docker-images / build-cli-docker-images / Publish CLI to Docker Hub	19m 26s
	2h 6m 22s

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