Separate construction/destruction for the sink output plugin core and the GUI

sdrbase/plugin/plugininterface.cpp

@@ -1,4 +1,5 @@
 #include "dsp/devicesamplesource.h"
+#include "dsp/devicesamplesink.h"
 #include "plugin/plugininterface.h"
 #include "plugininstanceui.h"
 
@@ -18,3 +19,7 @@ void PluginInterface::deleteSampleSinkPluginInstanceGUI(PluginInstanceUI *ui)
     ui->destroy();
 }
 
+void PluginInterface::deleteSampleSinkPluginInstanceOutput(DeviceSampleSink *sink)
+{
+    sink->destroy();
+}