PERF: no need to check for DataFrame in pandas.core.computation.expressions
In practice, this case is only covered by specific tests using DataFrame in `test_expressions.py`, not from actual usage through ops (so I just updated the failing tests to not use any DataFrame as input to those checks). 
Although our test suite might not be the best suited to check that, since many tests are small and thus don't use the numexpr path... (fixing that in https://github.com/pandas-dev/pandas/pull/40463)