This reverts commit 080751a.

Previously we used `http.DefaultTransport` (on which this is based),
but this uses a default dial timeout of 30s, which when we (by default)
wrap things in 5x retries can lead to ~150s delays simply pinging
an http-based registry.

If folks encounter issues with this via the library they can restore
the current behavior with:
```go
remote.WithTransport(http.DefaultTransport)
```

If folks encounter issues with this via `crane` they can restore the
current behavior with:
```
--dial-timeout 30s
```