epath depends on backport package importlib_resources

etils.epath depends on the `importlib_resources` library [here](https://github.com/google/etils/blob/8807c1997cbb3d5884551ddf786cefd776ff18a4/etils/epath/resource_utils.py#L31).

`importlib_resources` is a backport library of the standard library `importlib.resources` for `python<3.9`. If I'm not mistaken, in all Python versions supported by etils, that's no longer necessary; instead one should just use the standard library `importlib.resources`.

I believe the current code leads to issues with some packaging tools like [pex](https://pex.readthedocs.io/en/v2.1.63/index.html), which are "smart" about not installing backport packages. This makes it difficult to use `etils` with such tools.