Removes reference to register_uninstall_hook from code comment

Perhaps mention uninstall.php in stead?

```
// Register hooks that are fired when the plugin is activated or deactivated.
// When the plugin is deleted, the uninstall.php file is loaded.
```
Mention uninstall.php in code comment
Merge pull request #77 from barryceelen/patch-1

Removes reference to register_uninstall_hook from code comment