Revert "Enable JULIA_DEBUG=Main in CI"

This reverts commit 733658e.

Author: tkf

.github/workflows/CI.yml

@@ -37,7 +37,6 @@ jobs:
         run: python -m tox -- --cov=diffeqpy -s
         env:
           TOXENV: py
-          JULIA_DEBUG: Main
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v1
         with: