package/scons: remove python from SCONS

package/scons: remove python from SCONS

Remove $(HOST_DIR)/bin/python from SCONS variable to allow each scons
package to select their python interpreter. Indeed, most of the scons
packages (alljoyn, benejson, gpsd) only supports python2

Fixes:
 - http://autobuild.buildroot.org/results/b45f9fb69615b80758adeff4571e170c3bd9356b
 - http://autobuild.buildroot.org/results/13144a7ebd64ef7889312053f06a14047eea232d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>