ui: webauthn registration: adapt error messages

ui: webauthn registration: adapt error messages

There are variuos hints that 'InvalidStateError' can be assumed to
come from an already registered token[0][1].

So indicate that more strongly, also omit the extra line and warning
triangle, there's already an error icon present.

[0]: step 2: https://w3c.github.io/webauthn/#sctn-registering-a-new-credential
[1]: step 3: https://w3c.github.io/webauthn/#sctn-op-make-cred

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>