fido2 desktop login, improve wording, remove link

[daringer]

File: [components/nitrokeys/features/u2f/desktop-login.rst] https://docs.nitrokey.com/components/nitrokeys/features/u2f/desktop-login.html

Nitrokey FIDO2 configured following these instructions.

is not properly worded - it should be more like "A FIDO2 capable Nitrokey like ...." (no need to configure the FIDO2 token here)