If using WIFI_INIT_CONFIG_DEFAULT, error message will point out lack of WiFi. Otherwise linker errors on WiFi symbols should help give a clue as to what is broken. Piggy-backs on changes in !420, ref github #230 #237
Removes redundant menu options, splits WiFi configuration out from generic ESP32 configuration.
1. remove sdp demo. 2. add sdkconfig.default for bt demos