gh-93910: Fix enum performance regression (GH-94614)

This removes the performance regression in 3.11, **at the expense of not fixing
the "bug" that allows accessing values from values** (e.g. `Color.RED.BLUE`).

Using the benchmark @markshannon [presented](https://github.com/python/cpython/issues/93910#issuecomment-1165503032), the results are:

| Version | Enum | Fast enum | Normal class |
| --- | --- | --- | --- |
| 3.10 | 2.04 | 0.59 | 0.56 |
| 3.11 | 2.78 | 0.31 | 0.15 |
| This PR | 1.30 | 0.32 | 0.16 |

I share this mostly as information about the source of the regression, as this may be useful. It may be that the lower-risk approach for the beta is just to revert to a previously-known working state.