remove unused `throughput_stress` folder #1705

Job	Run time
test-omes	1m 46s
build-worker (java)	3m 1s
check-worker (dotnet)	1m 24s
build-worker (go)	1m 37s
check-worker (typescript)	2m 5s
build-cli	2m 1s
check-worker (python)	56s
prepare-for-docker-push	6s
build-worker (python)	2m 7s
build-worker (typescript)	2m 48s
build-worker (dotnet)	2m 13s
test-kitchensink (python)	2m 1s
check-worker (go)	1m 7s
check-worker (java)	2m 4s
test-kitchensink (typescript)	2m 39s
test-kitchensink (dotnet)	2m 26s
test-kitchensink (java)	4m 52s
build-ks-gen-and-ensure-protos-up-to-date	1m 25s
test-kitchensink (go)	2m 8s
push-docker-images / build-go-docker-images / Publish go to Docker Hub	10m 3s
push-docker-images / build-cli-docker-images / Publish CLI to Docker Hub	20m 7s
push-docker-images / build-python-docker-images / Publish python to Docker Hub	11m 49s
push-docker-images / build-dotnet-docker-images / Publish dotnet to Docker Hub	13m 9s
push-docker-images / build-java-docker-images / Publish java to Docker Hub	17m 54s
push-docker-images / build-typescript-docker-images / Publish typescript to Docker Hub	16m 28s
	2h 8m 16s

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