[R] R to Arrow to R roundtrip adds a `ptype` column attribute to list columns

### Describe the bug, including details regarding any error messages, version, and platform.

```r
> df <- data.frame(a=1:2, b=I(list(list("a","b"), list("ab","bc","cd","de"))))
> arrow::write_feather(df,"df")
> df2 <- arrow::read_feather("df")
> attributes(df$b)
$class
[1] "AsIs"

> attributes(df2$b)
$class
[1] "AsIs"

$ptype
[0]>
```

### Component(s)

R