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)
cc @jreback you might be more familiar with the history behind this. I suppose at some point, DataFrames were passed directly to `evaluate` in `expressions.py`. But now we are only passing arrays from `array_ops.py`, so I just updated the tests. @jreback OK here? thanks @jorisvandenbossche 