tls: remove Curl_ssl false_start

The secure transport vTLS backend was the only Curl_ssl struct instance
that populated the false_start field. Since its removed, we can now
remove that field entirely. This was a protocol feature specific to TLS
1.2 that has been replaced by the more widely adopted TLS 1.3 early data
mechanisms.

--false-start is now deprecated

Closes #17595

src/tool_cfgable.h

@@ -330,7 +330,6 @@ struct OperationConfig {
   BIT(proxy_ssl_auto_client_cert); /* proxy version of ssl_auto_client_cert */
   BIT(noalpn);                    /* enable/disable TLS ALPN extension */
   BIT(abstract_unix_socket);      /* path to an abstract Unix domain socket */
-  BIT(falsestart);
   BIT(path_as_is);
   BIT(suppress_connect_headers);  /* suppress proxy CONNECT response headers
                                      from user callbacks */