Dropping pkg_resources

[jakirkham]

Currently this uses pkg_resources, which is planned to go away:

streamz/streamz/plugins.py

Line 3 in b73a8c4

import pkg_resources

The code using it mainly uses the iter_entry_points function:

streamz/streamz/plugins.py

Lines 17 to 22 in b73a8c4

	for entry_point in pkg_resources.iter_entry_points("streamz.sources"):
	try_register(cls, entry_point, staticmethod)
	for entry_point in pkg_resources.iter_entry_points("streamz.nodes"):
	try_register(cls, entry_point)
	for entry_point in pkg_resources.iter_entry_points("streamz.sinks"):
	try_register(cls, entry_point)

This could be replaced by importlib.metadata.entry_points, which has been around since Python 3.8.