R1:ee7879e6267b

Change bin/storage destroy to be less scary when removing test data

Summary: I've pulled up this code probably three different times to make sure that the big scary warning does, in fact, still get printed even when passing `--unitest-fixtures` to `bin/storage destroy`. Make the warning message less scary if only removing test data.

Test Plan: Ran with and without `--unitest-fixtures` and saw expected warnings. After agreeing to warnings, test data was deleted as expected. Did not test `bin/storage…