What are the .android folders and adbkey files on my computer?

If your computer has never had an Android device connected, then I don't know where those files came from.

On my computer (as I use both Android and its SDK) those files are an SSH key-pair that allow me to mark my computer as "trusted" to my phone.

SSH keys shouldn't be harmful.

If you want to verify that these are SSH keys, open ".android" in the file browser (Nautilus), right-click on "adbkey", and select Properties. The file's Type should be "PKCS#8 Personal Key in PEM format (application/pkcs8+pem)" and its Size exactly 1,704B. "adbkey.pub" should be a little over 700B.

("adbkey.pub" is unhelpfully described as a Microsoft Publisher file: I put this down to Nautilus making a guess from the extension; equally unhelpfully, the file command describes them both as "ASCII text".)

I can attach a sample copy of each file, if you want to confirm yours have the correct format.