REST API returns backendServiceUrl

Related to the question I asked in #270, I'm calling the new developer portal REST API `/apis` endpoint from our site, and it returns an array of api entities. The `properties` object includes a `serviceUrl` that contains the URL to the backend API:

For example:
```
"value": [
{
"id": "/subscriptions/xxx/resourceGroups/xxx/providers/Microsoft.ApiManagement/service/xxx/apis/12345",
"type": "Microsoft.ApiManagement/service/apis",
"name": "some-api",
"properties": {
"displayName": "Some API",
"apiRevision": "1",
"description": "Some API description.",
**"serviceUrl": "https://someapi...",**
"path": "someapi",
"protocols": [
"https"
],
"authenticationSettings": null,
"subscriptionKeyParameterNames": null,
"isCurrent": true
}
}
. . .
],
"count": ...
}
```
I wonder why is the `serviceUrl` included here?

I'd rather not have the backend API URL leaked out and sent down to the client - the new developer portal won't be talking directly to the API backend, and anyone sniffing the network traffic in the browser debugger would be able to discover the URL of the API backend itself (not callable of course, but seems odd to unnecessarily leak it this way).

Any thoughts on perhaps removing that property from the developer-facing portal REST API responses?

Locate the developer portal REST API `/apis` entry point and inspect how API entities' `properties` are shaped. Reproduce the response shown, then verify that developer-facing `/apis` responses omit `serviceUrl` while retaining the other listed properties and that any relevant response checks pass.

Written by the indexing model from the issue text.