`entry_list` never user

The variable `entry_list` (https://github.com/pwang7/rebook/blob/master/rebook.py#L2070) is never used.

```
entry_list = [
    inputPathEntry,
    outputPathEntry,
    cmdArgEntry,
    pageNumEntry,
    landscapePageNumEntry,
    currentPreviewPageNumEntry,
]
```

I think you can remove it