feat: clean up unused DB table service_provider

[peterhaochen47]

• This table was added for the UAA-as-SAML-IDP feature (b93c87a)
• This feature has been removed: Remove SAML IDP feature #2638. Hence this table is now unused.
• The "DROP TABLE IF EXISTS" syntax would not error out if the table does not exist, compared to just "DROP TABLE".
• Also clean up docs and a test util that reference this table.

[#182118433]

[cf-gitbot]

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

https://www.pivotaltracker.com/story/show/186960080

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

[Tallicia]

Looks good

[Tallicia]

@strehle FYI - I believe this is expected to be included before the v77 release as part of the breaking changes for the SAML IdP removal.

[strehle]

@peterhaochen47 I have seen this also during review of #2638 but I thought you wanted wait with the removal.

My assumption was that maybe we wait an additional release until removing the DB table because if we remove data we cannot revert to the older version.
Assume: someone does a CF update but then realizes that SAML IDP is not available anymore. If they then go back to the UAA before they can run without disruption. If we remove the DB table we remove this possiblity.

Therefore I thought it was wanted to not removing the table, however from my side we can also remove it and then release or
release now 77.v

[strehle]

OK for SAP, but see my comments about this step.... if we delete the table, then the way back is not possible

[hsinn0]

I am also for not removing the table right away but waiting for a couple of releases or so.

[peterhaochen47]

Given that this PR has 2 approvals (and that I just discussed this with my team and the team was mostly neutral but leaning toward merging), so I will opt to merge this & include it in UAA v77.0.0.