Delete a previously created QSocketNotifiers.
Delete a previously created QSocketNotifiers.

Delete notifiers on close in Unix engine to avoid a descriptor mismatch for next open.

Change-Id: I21ba89933161004d721e172ad9f7c01fa4b85fa2
Reviewed-by: Laszlo Papp <2164cc32668ec579454611fc5261234262c80421@kde.org>
Reviewed-by: Denis Shienkov <1ad2dee90c89b865e4a01188e9919a005e3f77cf@yandex.ru>

RoadWorksSoftware/QtSerialPort-OS2,kobolabs/qtserialport,kobolabs/qtserialport,RoadWorksSoftware/QtSerialPort-OS2