A couple of minor improvements to connector-files

* read from FTP in binary mode for hash correctness
* tweak call to write to make it 8.0 compatible
I think it was because context was passed to write() and the new API does not handle that.

When we use `write()`  directly on a `browse_record`, we don't need to pass the `context` argument because it uses the one that is stored inside the `browse_record`.

Correct:
```
invoice.write(vals)
```
Wrong or useless:
```
invoice.write(vals, context=context)
```