[integration_test] Deprecate, and stop using in this repository

[stuartmorgan]

• Updates integration_test README to note that the published version is deprecated and direct people to the SDK version.
• Updates all plugins here to use the SDK version.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

[stuartmorgan]

This doesn't update the version and CHANGELOG of all the plugins it touches since I would not expect this to be a change that matters in the published version, thus shouldn't need publishing. If there's a reason we need to publish that I missed, I can update the PR accordingly.

[ditman]

At some point, we need to ask people to unpublish this, maybe? https://pub.dev/packages/integration_test Or mark it as "deprecated"?

[stuartmorgan]

Yes, I was going to publish this now to guide people via the README, then eventually (I need to think about how long to wait) mark it as discontinued.

[ditman]

@stuartmorgan I've seen that pub.dev redirects to the flutter API docs for some packages. I'm not sure how that's achieved, but check out this link: http://pub.dev/packages/flutter_test. It'd be nice that integration_test eventually redirected to api.flutter.dev as well!

[stuartmorgan]

Oh, that's nice! @jonasfj what's the mechanism for adding a redirect like that?