scd:nks: Don't flag the ESIGN keypair EF as encryption capable.

* scd/app-nks.c (filelist): Tweak 0x4531.

Actually the certificate has no encryption usage but we should also
tell that via KEYINFO so that this key is never tried to create an
encryption certificate.

(cherry picked from commit 3a2fb1c30633373d17880469e0b84ab2a9524585)