Don't warn about /simple/ fallback for PyPI

and display a little more info about the index used.

##### Before

```
$ pip install thispackagedoesntexist
Collecting thispackagedoesntexist
  DEPRECATION: One or more of your dependencies required using a deprecated fallback to looking at /simple/ to discover it's real name. It is suggested to upgrade your index to  support normalized names as the name in /simple/{name}.
  Could not find any downloads that satisfy the requirement thispackagedoesntexist
  No distributions at all found for thispackagedoesntexist
```

##### After

```
$ pip install thispackagedoesntexist
Collecting thispackagedoesntexist
  Could not find any downloads that satisfy the requirement thispackagedoesntexist
  No distributions at all found for thispackagedoesntexist
```