Update private Docker registry docs: remove GCR, focus on Docker Hub and AWS ECR

Author: Hkhan161

cerebrium/container-images/private-docker-registry.mdx

@@ -3,7 +3,7 @@ title: "Using Private Docker Registries"
 description: "How to authenticate, pull, and use private Docker images as base images in your deployments."
 ---
 
-Cerebrium supports using your own private Docker images as base images for your deployments - including images from Docker Hub, AWS ECR, Google Container Registry, or any Docker-compatible private registry.
+Cerebrium supports using your own private Docker images as base images for your deployments - including images from Docker Hub and AWS ECR.
 
 Our build system securely pulls your private image using the Docker credentials stored in your ~/.docker/config.json, and then builds your app on top of that image. Since these credentials are used during deployment, they should be team-accessible rather than tied to a single individual.
 
@@ -33,12 +33,6 @@ aws ecr get-login-password --region us-east-1 | \
   123456789.dkr.ecr.us-east-1.amazonaws.com
 ```
 
-**Google Container Registry:**
-
-```bash
-gcloud auth configure-docker
-```
-
 **Generic Registry:**
 
 ```bash