[functorch] Remove test/test_functorch_lagging_op_db.py (pytorch/functorch#845)
These tests are expected to fail, but we didn't communicate that very
well and:
1. we have gotten multiple questions about them
2. we need to special case it in our CI
3. we don't even use the test anymore!
So we are deleting it.
Related: https://github.com/pytorch/functorch/issues/835
