CC0017 Change to auto property codefix removes multiple variable declaration.

While I was working on #500 I encountered another issue:
## CodeFix removes multiple variable declaration.

The following:

``` CSharp
public int x, y;
public int X
{
    get { return x; }
    set { x = value; }
}
```

Get transformed into

``` CSharp
public int X { get; set; }
```

The `y` gets removed.
