qtdemux: Do not use unreliable framerate
qtdemux: Do not use unreliable framerate

timescale/1 is unreliable value for framerate. Due to downstream
element usually use framerate generated by qtdemux, let it be omitted
until the framerate can be reliably calculated.

https://bugzilla.gnome.org/show_bug.cgi?id=764733

Kurento/gst-plugins-good,Kurento/gst-plugins-good,Kurento/gst-plugins-good,Kurento/gst-plugins-good,Kurento/gst-plugins-good