@description should not be suggested or allowed on metadata

1) The following should give an error because @description has no effect on the generated template:
```bicep
@description('description')
metadata foo  = 'foo'
```
2) The following should not suggest adding @description:
<img width="332" alt="image" src="https://github.com/Azure/bicep/assets/6913354/0915aab1-bab9-4dab-8110-3c6927ad0314">