BTreeFolder2: do not patch manage_delAllObjects on Zope2

On Zope2 this method does not exist and this caused a test failure

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FAIL: test_method_protection (testSecurity.TestSecurity)
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Traceback (most recent call last):
  File "parts/erp5/Products/ERP5/tests/testSecurity.py", line 110, in test_method_protection
    self.fail(message)
AssertionError:
The following 1 methods have a docstring but have no security assertions.
	parts/erp5/product/ERP5Type/patches/BTreeFolder2.py:111 manage_delAllObjects