curl: ssh_config_matches is dead code: unauthorized SSH key reuse

Summary libcurl's SSH connection-reuse guard sshconfigmatches — added for CVE-2022-27782 and reaffirmed by CVE-2023-27538 — is dead code in every release since 7.83.1. It compares sshc-rsa / sshc-rsapub between a new transfer "needle" and a pooled connection, but on both sides those pointers are...