use legacy setuptools build meta

Author: vidartf

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
 requires = ["jupyterlab~=3.0", "setuptools>=40.8.0", "wheel"]
-build-backend = "setuptools.build_meta"
+build-backend = "setuptools.build_meta:__legacy__"

setup.py

@@ -3,12 +3,7 @@
 
 HERE = Path(__file__).parent.resolve()
 
-try:
-    import setupbase
-except:
-    import sys
-    import os
-    sys.path += [str(HERE)]
+import setupbase
 
 from setupbase import (
     log,