Update P4 config & readme

Author: AdrianSoundy

targets/ESP32/_IDF/sdkconfig.default.esp32p4

@@ -20,8 +20,6 @@ CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="targets/ESP32/_IDF/${TARGET_SERIES_SHORT
 CONFIG_COMPILER_OPTIMIZATION_SIZE=y
 CONFIG_COMPILER_OPTIMIZATION_ASSERTIONS_DISABLE=y
 
-CONFIG_SLAVE_IDF_TARGET_ESP32C6=y
-
 # Bluetooth currently not building with hosted/remote config
 CONFIG_BT_ENABLED=y
 CONFIG_BT_NIMBLE_ENABLED=y