Remove DocCReferenceResolutionService

[ahoppen]

I wanted to fix build warnings due to the deprecation of OutOfProcessReferenceResolver.Request in favor of RequestV2 but realized that DocCReferenceResolutionService.resolve was never called in any of the test cases, so it seems that we can completely remove it, unless I missed something.

[ahoppen]

@swift-ci Please test

[matthewbastien]

The DocCReferenceResolutionService is needed to show the Topics at the bottom of the documentation preview (as well as for highlighting links in the documentation). We could omit it for simplicity's sake, but it would mean that the live preview will not match the actual generated documentation.

Here's what the live preview looks like in VS Code before this change. I've highlighted the differences in red:

Here's what it looks like after this change:

[matthewbastien]

You bring up a good point about tests. We should add some if we intend on keeping this.

[ahoppen]

OK, in that case we shouldn’t remove it. Closing this PR.