Revert release branch only commit after merge

This is a revert of a revert, because the initial revert is only
supposed to be in the release branch.

This reverts commit 3eed00dc54.

source/blender/python/mathutils/mathutils_kdtree.c

@@ -394,7 +394,7 @@ PyTypeObject PyKDTree_Type = {
     /*tp_setattro*/ NULL,
     /*tp_as_buffer*/ NULL,
     /*tp_flags*/ Py_TPFLAGS_DEFAULT,
-    /*Documentation string*/ py_KDtree_doc,
+    /*tp_doc*/ py_KDtree_doc,
     /*tp_traverse*/ NULL,
     /*tp_clear*/ NULL,
     /*tp_richcompare*/ NULL,