Trackbacks was a silly feature in MediaWiki that I removed back rSVN104051 -- almost 6 years ago. It was never used at WMF and all tables should already be empty--nothing references it and if it does then it deserves to be broken :p
Kill it with the fire of 1000 suns.
- s1 (enwiki doesn't have it, someone must've dropped it years ago)
- s2 (itwiki, zhwiki, eowiki all have it--assuming most will)
- s3 (most probably will have it)
- s4 (commonswiki has it)
- s5 (dewiki does, wikidatawiki doesn't)
- s6 (all 3 wikis here have the table)
- s7 (eswiki, huwiki, arwiki all do--assuming most will)