Revert "Prevent intermittent GitHub Actions failures on Windows by setting MPLBACKEND=Agg per https://github.com/orgs/community/discussions/26434#discussioncomment-3251926 - NREL#365" - doesn't work

This reverts commit fa32232.

Author: softwareengineerprogrammer

tests/__init__.py

@@ -1,10 +0,0 @@
-import os
-
-import matplotlib as mpl
-
-if os.name == 'nt' and 'TOXPYTHON' in os.environ:
-    # Backend should be 'Agg' in GitHub Actions to prevent intermittent Windows failures
-    # per https://github.com/NREL/GEOPHIRES-X/issues/365
-    mpl.use('Agg')
-
-print(f'[DEBUG] matplotlib backend: {mpl.get_backend()}')