Clean up extension oddities

[iinuwa]

There's a couple things we should clean up with the web extension

• we should skip conditional create while we don't support it.
• PRF doesn't work from the extension for some reason, though I think it works in the Flatpak version.

[AlfioEmanueleFresta]

Updated description as I remember reviewing #176.

As for PRF: this should only involve testing, and ensuring the extension is passing the extensions JSON object as expected to credentialsd.