Selling water damaged MacBook Air 2017: Is it safe to simply remove the SSD?
Yes, you can assume that none of your data is still on the MacBook Air. All personal data stored on the laptop itself is stored on the SSD, so removing this effectively removes the data from the laptop.

It is also possible that the SSD is still fully functioning, so if you made the mistake of not backing up your data, you may be able to still access it from the SSD, via adaptors, external enclosures or another MBA of the same generation.

You may also want to refer to Apple's advice on what to do before you sell, give away, or trade in your Mac.