[PyROOT] Set memory policy to "strict"

PyROOT has many memory leaks, which is a major pain point for people
using it for long-running scripts in batch jobs.

One source of memory leaks was indentified to be the "heuristic memory
policy" of PyROOT. This means that PyROOT assumes that every non-const
pointer member function argument was interpreted as the object taking
ownership if the argument.

For examle, take the non-owning RooLinkedList container. It has a
`RooLinkedList::Add(RooAbsArg *arg)` method. PyROOT wrongly assumes that
this means the RooLinkedList takes ownership of arg, and it drops the
PyROOT overship. Nobody feels responsible for deleting the object
anymore, and there is a memory leak or `arg`.

That particular leak was reported in this forum post:
https://root-forum.cern.ch/t/memory-leak-in-fits/56249

Function parameters of type `T *` are very common in ROOT, and only
rarely do they imply ownership transfer. So changing the memory policy
to "strict" would surely fix also many other memory leaks that are not
reported so far. In fact, upstream cppyy doesn't even have this
heuristic memory policy anymore! So moving PyROOT also to the strict
memory policy closes the gap between PyROOT and cppyy.

The potential drawback of this change are crashes in usercode if memory
is not properly managed. But these problems should either be fixed by:

  * the user

  * dedicated pythonizations for these methods to manage shared
    ownership via Python reference counters (i.e., setting the parameter
    as an attribute of the object that the member function was called
    on)

This follows up on PR #4294, in particular it reverts 3a12063.

Author: guitargeek

bindings/pyroot/pythonizations/python/ROOT/_facade.py

@@ -204,11 +204,6 @@ def _finalSetup(self):
         if not self.gROOT.IsBatch() and self.PyConfig.StartGUIThread:
             self.app.init_graphics()
 
-        # Set memory policy to kUseHeuristics.
-        # This restores the default in PyROOT which was changed
-        # by new Cppyy
-        self.SetMemoryPolicy(self.kMemoryHeuristics)
-
         # Redirect lookups to cppyy's global namespace
         self.__class__.__getattr__ = self._fallback_getattr
         self.__class__.__setattr__ = lambda self, name, val: setattr(gbl_namespace, name, val)