stop using deprecated ElementTree methods "getchildren()" and "getiterator()"
stop using deprecated ElementTree methods "getchildren()" and "getiterator()"

Both methods were removed in Python 3.9 as mentioned in the release notes:

> Methods getchildren() and getiterator() of classes ElementTree and Element in
> the ElementTree module have been removed. They were deprecated in Python 3.2.
> Use iter(x) or list(x) instead of x.getchildren() and x.iter() or
> list(x.iter()) instead of x.getiterator().

python-babel/babel,python-babel/babel,mitsuhiko/babel,mitsuhiko/babel,mitsuhiko/babel