Makefile: Stop building Python for Xen 4.5 or later.

Makefile: Stop building Python for Xen 4.5 or later.

We still bundle Python code even if we do not need. In
the past the only reason for doing it was for Xend but
since that is gone..

However the python-dependency brought in some other dependencies
shared by other programs - gdb and perl. As such make this
dependency be part of the targets.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>