Wrong labels values queries filtering when already selected.

#### Describe the bug

When trying to list labels values for a label name already set to filter in the query, we currently use the label value as a filter and return therefore only that values

See the HTTP request generated when I have the `unspecified` service name selected:

```
POST http://localhost:4040/querier.v1.QuerierService/LabelValues
....
{"matchers":["{__profile_type__=\"process_cpu:cpu:nanoseconds:cpu:nanoseconds\", service_name=\"unspecified\"}"],"name":"service_name"}

200 OK
{"names":["unspecified"]}

````

#### To Reproduce

Try to list all services when the services is already selected.

#### Expected behavior

I should see all available services even though I have one selected.

#### Environment

- Infrastructure: [e.g., Kubernetes, bare-metal, laptop]
- Deployment tool: [e.g., helm, jsonnet]

#### Additional Context