aggregator: Flushing is always in pad lock, no need to atomics
aggregator: Flushing is always in pad lock, no need to atomics

The usage of atomics was always doubtful as it was used to release a
GCond

https://bugzilla.gnome.org/show_bug.cgi?id=747220

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer