warning: A function declaration without a prototype is deprecated in all versions of C (dc_event_channel_new)

This new function `dc_event_channel_new` gives a warning that "A function declaration without a prototype is deprecated in all versions of C"

it suggests the following

```diff
- dc_event_channel_t* dc_event_channel_new();
+ dc_event_channel_t* dc_event_channel_new(void);
```

but I do not know C so I don't know what this change actually does.