Back in commit
f72be49830 ("package/scons: remove
python from SCONS"), we changed the SCONS variable to not explicitly
invoke the Python interpreter, because some scons-based packages used
python2, some python3.
Now that the 3 remaining packages using scons (gpsd, mongodb and
benejson) all use python3, we can bring back the python3 interpreter
call into the SCONS variable, and slightly simplify those packages.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>