Inline ChangeRequestSCMHead2 interface into ChangeRequestSCMHead

[das7pad]

This PR is cleaning up the ChangeRequestSCMHead/ChangeRequestSCMHead2 interface workaround that was needed back before Java 8.

Testing done

I've reviewed the usages of ChangeRequestSCMHead in the jenkinsci org and did not spot any instances that would not satisfy the ChangeRequestSCMHead2 requirement. So we could remove the default implementation as well.

Submitter checklist

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• Ensure that the pull request title represents the desired changelog entry
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[jglick]

There are usages right in this plugin that would need to be adapted, namely

scm-api-plugin/src/main/java/jenkins/scm/api/mixin/ChangeRequestSCMRevision.java

Lines 79 to 80 in 24df4bb

	return !(head instanceof ChangeRequestSCMHead2)
	|| ((ChangeRequestSCMHead2) head).getCheckoutStrategy() != ChangeRequestCheckoutStrategy.HEAD;

and then I think a downstream PR would need to be prepared for https://github.com/jenkinsci/branch-api-plugin/blob/e73a56d397882c63ae06483ba81742c2e39d25d5/src/main/java/jenkins/branch/BranchNameContributor.java#L73-L75

[jglick]

Should it not be deprecated?

[timja]

Can it be DoNotUse? That way it blocks usages in this plugin too?

Suggested change

	@Restricted(NoExternalUse.class)
	@Restricted(DoNotUse.class)

[jglick]

@Restricted is inappropriate. It is simply @Deprecated.

[das7pad]

There are usages right in this plugin that would need to be adapted, namely

Thanks for the pointers, that's addressed in d8d6da5. I've also switch the annotation to @deprecated in d2ec56f.

and then I think a downstream PR would need to be prepared for https://github.com/jenkinsci/branch-api-plugin/blob/e73a56d397882c63ae06483ba81742c2e39d25d5/src/main/java/jenkins/branch/BranchNameContributor.java#L73-L75

👍 I've opened a PR over there:

• Adopt flattened interface for ChangeRequestSCMHead branch-api-plugin#821