It’s an adjective and it means not having or lacking enthusiasm. If someone is unenthusiastic about something it means they are feeling indifferent, apathetic, passive, phlegmatic, lukewarm, listless, languid, lethargic, emotionless, perfunctory about it.
This phrase makes an appearance in Phoenix Wright: Ace Attorney - Turnabout Samurai. It is stated by the best prosecutor in the Ace Attorney series, Miles Edgeworth.
Unnecessary Feelings has a celebration day on 20th October, usually people will make fanart of the scene and post on social media to celebrate.
Miles Edgeworth: Thanks to you, I am saddled with unnecessary... feelings.
The assumption is that all involved heard/read what was said (as would usually be the case on small Usenet newsgroups), all agreed upon it enough not to object, and no one had any objections, so the statement is presumed to have been heard and acknowledged.