[plugins] drop backport of importlib.metadata (importlib_metadata)

since we don't support < python 3.10 we can safely use importlib.metadata (https://importlib-metadata.readthedocs.io/en/latest/)

src/pyxu/info/plugin.py

@@ -1,6 +1,5 @@
 import warnings
-
-from importlib_metadata import entry_points
+from importlib.metadata import entry_points
 
 import pyxu.info.warning as pxw