cpu/esp: revert the change for ESP_WIFI_PASS define

Previously, a default value for ESP_WIFI_PASS was intentionally defined only if DOXYGEN was also defined, to allow ESP_WIFI_PASS to be left undefined for using APs without authentication. With PR #17415 the definition was changed to always define a default value for EPS_WIFI_PASS.  This made it impossible to use APs without authentication. The commit reverts this change.

cpu/esp_common/esp-wifi/esp_wifi_params.h

@@ -51,7 +51,7 @@
 /**
  * @brief   Passphrase used for the AP as clear text (max. 64 chars).
  */
-#ifndef ESP_WIFI_PASS
+#ifdef DOXYGEN
 #define ESP_WIFI_PASS       "ThisistheRIOTporttoESP"
 #endif