Remove related link from service instance sharing endpoint

[jenspinney]

As an app dev (sharer) I no longer get a related shared_spaces link in the shared spaces endpoint #153566266

NOTE: This PR builds on top of #1033, which should be merged first. The actual changes on top of #1033 can be viewed in this diff.

What

When we first implemented the POST /v3/service_instances/:guid/relationships/shared_spaces endpoint, we returned a response that looked like this:

{
  "data": [
    {
      "guid": "885de116-1313-46a3-a578-f152eea17af6"
    },
    {
      "guid": "05e472b8-ff7d-4f2f-bd00-dd874aa822eb"
    }
  ],
  "links": {
    "self": {
      "href": "https://api.example.com/v3/service_instances/ddaa57af-eeaf-4098-9f7e-31aad16c36f5/relationships/shared_spaces"
    },
    "related": {
      "href": "https://api.example.com/v3/service_instances/ddaa57af-eeaf-4098-9f7e-31aad16c36f5/shared_spaces"
    }
  }
}

As we're rounding out the API and filling in the gaps, we looked into implementing the GET endpoints to the two links listed in the links section. We found that the related link above is somewhat strange to implement and consume, since it would need to be heavily redacted if the querying user doesn't have full read permission to all the target spaces. This PR removes the related link. The work to implement the GET method on the self link, on the other hand, will be coming shortly in a following PR.

Changes:

• Removed related link from being return by the response of POST /v3/service_instances/:guid/relationships/shared_spaces
• Removed related link from documentation of this endpoint.

PR

• I have viewed signed and have submitted the Contributor License Agreement
• I have made this pull request to the master branch
• I have run all the unit tests using bundle exec rake
• I have run CF Acceptance Tests on bosh lite

Thanks,
SAPI team (@jenspinney and @ablease)

[cfdreddbot]

Hey jenspinney!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/153665574

The labels on this github issue will be updated when the story is started.

[anniesing]

Changes looks good. Docs looks good. Merging now.