Fix setup.cfg

Author: dstansby

setup.cfg

@@ -17,9 +17,6 @@ classifiers =
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.8
-    Programming Language :: Python :: 3.9
-    Programming Language :: Python :: 3.10
     Topic :: Software Development :: Testing
 project_urls =
     Bug Tracker = https://github.com/matplotlib/napari-matplotlib/issues