chardev subsystem/library doesn't use gnutls. Use the dedicated
chardev_ss.dependencies() instead.

Looking at history, it was added in commit 3eacf70b ("meson:
Propagate gnutls dependency") because crypto/tlscreds.h included
GnuTLS. This was cleaned-up later by commit 678bcc3c ("crypto:
Make QCryptoTLSCreds* structures private").

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220323155743.1585078-2-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>