python-can: remove incorrect dependency

When using the python-package infrastructure, there is no need for
packages to declare a dependency on the Python interpreter: the
package infrastructure does it automatically.

Moreover, this is actually broken in the case of python-can, which can
be selected either with Python 2.x or Python 3.x. If the latter is
chosen, python-can will still trigger the build of Python 2.x, which
is incorrect.

This was discovered by Vicente Olivert Riera during the analysis of
the following build failure:

  http://autobuild.buildroot.net/results/aff/affb1d4a328c479be73b7818364db5914bf3d376/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>