skel: Replace usage of pkg_resources with importlib.resources

[pdxjohnny]

Just came across this: https://docs.python.org/3/library/importlib.html#importlib.resources.path

We should get rid of some usages of pkg_resources within our codebase. This would make it so we could be zip_safe!

[Nishikoh]

Hi, I'd like to tackle that.

[pdxjohnny]

@Nishikoh Awesome! Just let me know, or anyone on Gitter if you need more info. This should be a case of finding all the pkg_resources.resource_filename and changing them

$ git grep pkg_resources | grep resource_
dffml/util/skel.py:    pkg_resources.resource_filename("dffml", "skel")
service/http/dffml_service_http/routes.py:    pkg_resources.resource_filename("dffml_service_http", "api.js")