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1.2 that has been replaced by the more widely adopted TLS 1.3 early data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

@@ -1999,7 +1999,7 @@ static ParameterError opt_bool(struct GlobalConfig *global,
     config->doh_verifystatus = toggle;
     break;
   case C_FALSE_START: /* --false-start */
-    config->falsestart = toggle;
+    opt_depr(global, a);
     break;
   case C_SSL_NO_REVOKE: /* --ssl-no-revoke */
     config->ssl_no_revoke = toggle;