Prefer default flash reading mode

Looking at the options at:
https://docs.espressif.com/projects/esp-idf/en/v4.0.1/api-reference/storage/spi_flash.html?highlight=dio%20dout#_CPPv414SPI_FLASH_DOUT
and the documentation for end users such as:
https://docs.espressif.com/projects/esp-idf/en/v4.0.1/api-guides/build-system-legacy.html?highlight=dio%20dout#save-flash-arguments
I think is better to prefer the default mode DIO over DOUT

Author: lulingar

docker/linux/Dockerfile

@@ -110,7 +110,6 @@ RUN bash -c "\
   source ./export.sh && \
   cd examples/get-started/hello_world && \
   make defconfig && \
-  echo "CONFIG_ESPTOOLPY_FLASHMODE_DOUT=y" >> sdkconfig && \
   idf.py bootloader partition_table"
 
 RUN mkdir /tools/blobs