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1.2 that has been replaced by the more widely adopted TLS 1.3 early data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

lib/urldata.h

@@ -295,7 +295,6 @@ struct ssl_config_data {
   char *key_type; /* format for private key (default: PEM) */
   char *key_passwd; /* plain text private key password */
   BIT(certinfo);     /* gather lots of certificate info */
-  BIT(falsestart);
   BIT(earlydata);    /* use tls1.3 early data */
   BIT(enable_beast); /* allow this flaw for interoperability's sake */
   BIT(no_revoke);    /* disable SSL certificate revocation checks */