fix: missing initializer warning in esp_eth

remove auto_nego_en member from esp_eth_config_t as it is not used
 anywhere

components/esp_eth/include/esp_eth.h

@@ -42,12 +42,6 @@ typedef struct {
     */
     uint32_t check_link_period_ms;
 
-    /**
-     * @brief Configuration status of PHY autonegotiation feature
-     *
-     */
-    bool auto_nego_en;
-
     /**
     * @brief Input frame buffer to user's stack
     *