remove `replica` mention in the init flow

The final text durnig init mentions being able to customize replica settings which is not valid in vnext: 

```
Added your agent as a service entry named 'env-var-cleanup' under the file azure.yaml.
  +  agent.yaml

You can customize environment variables, cpu, memory, and replica settings in the agent.yaml.
Next steps: Run azd deploy env-var-cleanup to deploy your agent to Microsoft Foundry.
```