There was only the now-unused FifoGatherer left, which could, if really
needed again, be re-instated near the actual worker that would need it.

Also, un-export LinuxDeviceDebugSupport and RemoteLinuxQmlProfilerSupport
which are not re-used, and conceptually not meant to be re-used, anymore.

Change-Id: I20b6eb2f4a85180b586ea8338cf74173e3b7b21c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>