I just checked every possible section that could be related to the delta flyer, and the ability to craft it at Memory Alpha. Non of the sections except for the page about the Delta Flyer itself make any reference to it being craftble.
The Delta Flyer page makes a note towards the bottom that references the fact that after season 5 hit, the Delta Flyer became c/z - store only.
It is a shame that the mission and the reward were removed, though.
LOL, I still have the schematics even though they aren't craftable anymore.
I should see what I can get for them on the Exchange
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The wiki isn't an official source of information, it is not updated by Cryptic devs. As a result, it is possible (and common) for it to have outdated or incorrect information, as the site relies entirely on players and random people to update it. Apparently nobody ever updated/removed the information about crafting the Delta Flyer, so it's still there.
I crafted my Delta Flyer the day before it was changed to a C-Store unlock. On the one hand, that means I have it on one of my characters. On the other hand, any of my other toons will be stuck with whatever other shuttles they can get, as I'm not going to go to the trouble of buying a C-Store shuttle when I never participate in shuttle events (possibly because I lack a good shuttle? Yay circular logic).