Revert "Update dartdoc to 0.43.0."
Revert "Update dartdoc to 0.43.0."

This reverts commit 076341b89aad0299afeee491b77d76657bb2056d.

Reason for revert: For some reason, this broke Golem?

Original change's description:
> Update dartdoc to 0.43.0.
>
> Release notes:  https://github.com/dart-lang/dartdoc/releases/tag/v0.43.0
>
> Change-Id: If60b856ef36a629d89534d5cc9a828b0782937ec
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/199501
> Reviewed-by: Samuel Rawlins <srawlins@google.com>
> Commit-Queue: Janice Collins <f6a8c838e29d3fa8813240c8bed106e760081e0e@google.com>

TBR=devoncarew@google.com,f6a8c838e29d3fa8813240c8bed106e760081e0e@google.com,srawlins@google.com

Change-Id: I74653fdaad44ff3729f85af0844f38818c7095b1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/199541
Auto-Submit: Janice Collins <f6a8c838e29d3fa8813240c8bed106e760081e0e@google.com>
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Commit-Queue: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk