Otherwise when pcscd doesn't terminate properly (ie. receive a SIGKILL),
it won't start again because of it's socket already existing.
* gnu/services/security-token.scm (pcscd-shepherd-service)[start]:
Remove existing socket file.
Fixes: <https://bugs.gnu.org/32478>.
* gnu/services/security-token.scm (pcscd-activation): Idempotently create the
/var/lib/pcsc symlink so that it does not fail when it already exists.
