simple: flag uses of strings.CutPrefix/CutSuffix that should use strings.TrimPrefix/TrimSuffix instead

Since the introduction of `strings.CutPrefix` and `strings.CutSuffix` I've started noticing code that should use `strings.TrimPrefix`/`strings.TrimSuffix` instead:

```
x, _ := strings.CutPrefix(y, "abc")
```

I just implemented the trivial analyzer for this for our internal lint tool. Might be a nice (tiny) addition to staticcheck.