sftp: libssh2 with gcrypt backend only supports deprecated key types

When connecting from Window or Macos, VLC will fail to connect on most servers:

May 21 09:42:40 server sshd[3866033]: Unable to negotiate with x.x.x.x port y: no matching host key type found. Their offer: ssh-rsa,ssh-rsa-cert-v01@openssh.com,ssh-dss>

Indeed, openssh deprecated some algorithm in https://www.openssh.com/txt/release-8.2 and most servers won't accept those provided by the current gcrypt backend of libssh2 anymore.

We probably need to find a solution for that before people re-add the deprecated algorithm to their ssh server so that they can continue using the access, in particular with VLC 4 indexing capabilities.