fix(cloudbuild): use PROJECT_ID instead of custom substitution

Author: robertodauria

cloudbuild.yaml

@@ -1,7 +1,6 @@
 substitutions:
   _REGION: us-east1
   _SERVICE_NAME: speed-proxy
-  _MLAB_PROJECT: mlab-sandbox
   _ALLOWED_ORIGIN: https://speed.measurementlab.net
 
 steps:
@@ -38,7 +37,7 @@ steps:
       - |
         sed -e "s|OTEL_IMAGE_PLACEHOLDER|${_REGION}-docker.pkg.dev/${PROJECT_ID}/m-lab/otel-collector:${BUILD_ID}|g" \
             -e "s|IMAGE_PLACEHOLDER|${_REGION}-docker.pkg.dev/${PROJECT_ID}/m-lab/${_SERVICE_NAME}:${BUILD_ID}|g" \
-            -e "s|MLAB_PROJECT_PLACEHOLDER|${_MLAB_PROJECT}|g" \
+            -e "s|MLAB_PROJECT_PLACEHOLDER|${PROJECT_ID}|g" \
             -e "s|ALLOWED_ORIGIN_PLACEHOLDER|${_ALLOWED_ORIGIN}|g" \
             service.yaml > service-deploy.yaml
         gcloud run services replace service-deploy.yaml \