Consolidate '{output-dir}' to the default 'service-dir'

Once all the languages adopt the 'emitter-output-dir' configuration in its emitter option, we would like to move the common `{output-dir}` part to the default `service-dir`. The plan is to have a batch PR to update all the existing 'tspconfig.yaml' in spec repos.

Sample of current config:
```yml
parameters:
"service-dir":
default: "sdk/contoso"
options:
"@azure-tools/typespec-csharp":
emitter-output-dir: "{output-dir}/{service-dir}/{namespace}"
flavor: azure
clear-output-folder: true
model-namespace: true
namespace: "Azure.ResourceManager.Contoso"
```