[DH-301] Remove outdated/unused gcr key

[shaneknapp]

since we no longer need gcr-key.json, we should remove it and all references of it from our repo.

(dh) ➜  deployments git:(staging) gcb remove-old-gcr-key
Switched to a new branch 'remove-old-gcr-key'
(dh) ➜  deployments git:(remove-old-gcr-key) find . | grep gcr | xargs git rm
rm 'deployments/a11y/secrets/gcr-key.json'
rm 'deployments/astro/secrets/gcr-key.json'
rm 'deployments/biology/secrets/gcr-key.json'
rm 'deployments/cee/secrets/gcr-key.json'
rm 'deployments/data100/secrets/gcr-key.json'
rm 'deployments/data101/secrets/gcr-key.json'
rm 'deployments/data102/secrets/gcr-key.json'
rm 'deployments/data8/secrets/gcr-key.json'
rm 'deployments/datahub/secrets/gcr-key.json'
rm 'deployments/dev/secrets/gcr-key.json'
rm 'deployments/dlab/secrets/gcr-key.json'
rm 'deployments/eecs/secrets/gcr-key.json'
rm 'deployments/gradebook/secrets/gcr-key.json'
rm 'deployments/highschool/secrets/gcr-key.json'
rm 'deployments/ischool/secrets/gcr-key.json'
rm 'deployments/julia/secrets/gcr-key.json'
rm 'deployments/logodev/secrets/gcr-key.json'
rm 'deployments/nature/secrets/gcr-key.json'
rm 'deployments/prob140/secrets/gcr-key.json'
rm 'deployments/publichealth/secrets/gcr-key.json'
rm 'deployments/r/secrets/gcr-key.json'
rm 'deployments/shiny/secrets/gcr-key.json'
rm 'deployments/stat159/secrets/gcr-key.json'
rm 'deployments/stat20/secrets/gcr-key.json'
rm 'deployments/ugr01/secrets/gcr-key.json'
rm 'deployments/workshop/secrets/gcr-key.json'
(dh) ➜  deployments git:(remove-old-gcr-key) cd ..
(dh) ➜  datahub git:(remove-old-gcr-key) grep -rinse gcr-key.json *
docs/admins/howto/new-hub.qmd:245:4. Copy gcr-key.json and gke-key.json from any other hub's secrets to the hub's secrets/
(dh) ➜  datahub git:(remove-old-gcr-key) vi docs/admins/howto/new-hub.qmd