Remove legacy python2 dependencies

[egede]

In a few helper and template scripts we in fact still use python2. This should be updated

GangaCore/Lib/Batch/BatchScriptTemplate.py.template:#!/usr/bin/env python2
GangaCore/Lib/Notebook/Notebook.py:                defvalue='python2',
GangaCore/test/GPI/Notebook/Test.ipynb:   "name": "python2"
GangaCore/test/GPI/Notebook/Test.ipynb:   "pygments_lexer": "ipython2",
GangaDirac/Lib/RTHandlers/ExeDiracRTHandler.py:    script_template = """#!/usr/bin/env python2
GangaLHCb/Lib/RTHandlers/ExeDiracRTHandler.py:    script_template = """#!/usr/bin/env python2

[souravpy]

Should this be updated to latest python version 3.14?

[egede]

Should this be updated to latest python version 3.14?

No, I think it should just be updated to say python3 instead of python2. And the scripts should be updated if they have something in them that is not python3 valid syntax. These are simple wrapper scripts, so they should be kept as "version agnostic" as possible as we do not have control of the exact version used (could be anything at the moment between 3.6 and 3.14).

[mesmith75]

Fixed by #2269