Make the importlib_metadata requirement unconditional

Author: rpanderson

setup.cfg

@@ -25,7 +25,7 @@ include_package_data = True
 packages = find:
 python_requires = >=3.6
 install_requires =
-  importlib_metadata ; python_version<'3.8'
+  importlib_metadata
   labscript_utils>=2.14.0
   numpy>=1.15
   scipy