python: Drop explicit version where possible

Some of our scripts are known to work both with Python 2 and
Python 3, so for them we shouldn't be forcing any specific
version of the interpreter when they're called directly; we
always use $(PYTHON) explicitly in our build rules anyway.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/apibuild.py

-#!/usr/bin/env python2
+#!/usr/bin/env python
 #
 # This is the API builder, it parses the C sources and build the
 # API formal description in XML.

docs/reformat-news.py

-#!/usr/bin/env python2
+#!/usr/bin/env python
 
 # reformat-news.py: Reformat the NEWS file properly
 #

src/esx/esx_vi_generator.py

-#!/usr/bin/env python2
+#!/usr/bin/env python
 
 #
 # esx_vi_generator.py: generates most of the SOAP type mapping code

src/hyperv/hyperv_wmi_generator.py

-#!/usr/bin/env python2
+#!/usr/bin/env python
 
 #
 # hyperv_wmi_generator.py: generates most of the WMI type mapping code