transport: remove `git_transport_smart_proxy_options`

Snuck in during refactoring; let's get rid of it.

include/git2/sys/transport.h

@@ -262,16 +262,6 @@ GIT_EXTERN(int) git_transport_smart_certificate_check(git_transport *transport,
 GIT_EXTERN(int) git_transport_smart_credentials(git_credential **out, git_transport *transport, const char *user, int methods);
 
 /**
- * Get a copy of the proxy options
- *
- * The url is copied and must be freed by the caller.
- *
- * @param out options struct to fill
- * @param transport the transport to extract the data from.
- */
-GIT_EXTERN(int) git_transport_smart_proxy_options(git_proxy_options *out, git_transport *transport);
-
-/**
  * Get a copy of the remote connect options
  *
  * All data is copied and must be freed by the caller by calling