ProjectExplorer: Make remove file dialog a bit wider

Makes it less probable that the 'Ok' button is below the 'Delete file
permanently' checkbox text (reducing accidents with it), and actually
looks nicer because wrapping for the file name kicks in less often.

Task-number: QTCREATORBUG-10616
Change-Id: If039edf3de36767e9cd6643d2465e029df4a5086
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>