Remove leftover references to 'nested iterators'
Remove leftover references to 'nested iterators'

As reported in #343: Nested iterators don't work as originally shown in the example.
The docstring of Table.where() has been correctly modified in 30f89b9fc5.
However, some references to that example were still in other docstrings.
avalentino/PyTables,joonro/PyTables,rdhyee/PyTables,mohamed-ali/PyTables,FrancescAlted/PyTables,tp199911/PyTables,gdementen/PyTables,rabernat/PyTables,joonro/PyTables,PyTables/PyTables,joonro/PyTables,andreabedini/PyTables,rabernat/PyTables,rabernat/PyTables,gdementen/PyTables,mohamed-ali/PyTables,andreabedini/PyTables,andreabedini/PyTables,tp199911/PyTables,mohamed-ali/PyTables,dotsdl/PyTables,mohamed-ali/PyTables,rdhyee/PyTables,PyTables/PyTables,rdhyee/PyTables,joonro/PyTables,jennolsen84/PyTables,rdhyee/PyTables,PyTables/PyTables,tp199911/PyTables,avalentino/PyTables,gdementen/PyTables,FrancescAlted/PyTables,dotsdl/PyTables,andreabedini/PyTables,gdementen/PyTables,avalentino/PyTables,dotsdl/PyTables,FrancescAlted/PyTables,dotsdl/PyTables,rabernat/PyTables,jennolsen84/PyTables,jennolsen84/PyTables,jennolsen84/PyTables,tp199911/PyTables