DAS: Comply with unintended_html_in_doc_comment

Change-Id: Ic96bb851e4f18d11badb3e429f5601e652f89b1a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/454162
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analysis_server/analysis_options.yaml

@@ -21,8 +21,6 @@ analyzer:
     implementation_imports: ignore
     overridden_fields: ignore
     todo: ignore
-    # Existing violations (361)
-    unintended_html_in_doc_comment: ignore
 
 linter:
   rules: