Problem/Motivation
We placeholder comment links which causes them to get built on every page view. This is likely unnecessary for the same reason as #2556767: Remove placeholdering of node links.
Found during profiling at #2552873: node/1 flamegraphs. See flame graph #1. This may be critical - we wont know much savings we'll get until after a patch is made (see #1744302: [meta] Resolve known performance regressions in Drupal 8).