Remove redunant function delaration.

include/mosquitto.h

@@ -1604,40 +1604,6 @@ libmosq_EXPORT int mosquitto_string_option(struct mosquitto *mosq, enum mosq_opt
  */
 libmosq_EXPORT int mosquitto_void_option(struct mosquitto *mosq, enum mosq_opt_t option, void *value);
 
-/*
- * Function: mosquitto_string_option
- *
- * Used to set const char* options for the client.
- *
- * Parameters:
- * mosq - a valid mosquitto instance.
- * option - the option to set.
- * value - the option specific value.
- *
- * Options:
- * MOSQ_OPT_TLS_ENGINE
- * Configure the client for TLS Engine support. Pass a TLS Engine ID
- * to be used when creating TLS connections.
- * Must be set before <mosquitto_connect>.
- * MOSQ_OPT_TLS_KEYFORM
- * Configure the client to treat the keyfile differently depending
- * on its type. Must be set before <mosquitto_connect>.
- * Set as either "pem" or "engine", to determine from where the
- * private key for a TLS connection will be obtained. Defaults to
- * "pem", a normal private key file.
- * MOSQ_OPT_TLS_KPASS_SHA1
- * Where the TLS Engine requires the use of a password to be
- * accessed, this option allows a hex encoded SHA1 hash of the
- * private key password to be passed to the engine directly.
- * Must be set before <mosquitto_connect>.
- * MOSQ_OPT_TLS_ALPN
- * If the broker being connected to has multiple services available
- * on a single TLS port, such as both MQTT and WebSockets, use this
- * option to configure the ALPN option for the connection.
- */
-libmosq_EXPORT int mosquitto_string_option(struct mosquitto *mosq, enum mosq_opt_t option, const char *value);
-
-
 /*
  * Function: mosquitto_reconnect_delay_set
  *