The comments schema, prior to December 2021, used parent_comment_id
instead of also storing top_comment_id. Comment pagination is based
now on top_comment_id. However, upstream never migrated their old
comments to populate tc_id, and thus retained two copies of pagination
logic, each using different limits to try to emulate similar behavior.
TheMotte foremost has no posts created prior to December 2021 (so
these branches never activated) and also has tc_id on all comments.
The dual limit pagination approach was already removed (there is
only one limit for paginating comments). This completes the removal of
this logic, since these are purely dead codepaths which have previously
caused confusion to contributors.
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