NUTTXNAME is used only as an alias for "nuttx", not actually a
configuration property. Its definition might erroneously imply that the
name of binary image may be configurable, which is not the case.
Redirect the first check of esptool to /dev/null as it will be printed
twice when esptool is called to convert the binary.
Signed-off-by: Abdelatif Guettouche <abdelatif.guettouche@espressif.com>
