Rename some `flake8-simplify` rules (#2915)
Renames the following rules that stood out to me at a glance as needing better names:
- `or-true` to `expr-or-true`
- `and-false` to `expr-and-false`
- `a-or-not-a` to `expr-or-not-expr`
- `a-and-not-a` to `expr-and-not-expr`
Related to #2902.
