Do not show (duplicate) hint for expired or revoked user IDs/keys

CertificateLineEdit that's used for additional encryption keys already
shows an error message for expired, revoked, disabled and otherwise
unusable (filtered out) user IDs/keys. The hint shown in the message
widget would duplicate this error message. Therefore, don't show it for
additional encryption keys that are expired or revoked (or disabled).
The hint is still shown for keys with expired, revoked, or otherwise
unusable encryption subkey because it's a bit more specific than the hint
shown by CertificateLineEdit.

• GnuPG-bug-id: T7789