timeline: simplify code to remove an object from the pendingobjects list
timeline: simplify code to remove an object from the pendingobjects list

g_list_remove_all () can be used as a simplification as the private data to ges
timeline object are 1:1.

cfoch/gst-editing-services,pitivi/gst-editing-services,cfoch/ges,cfoch/gst-editing-services,pitivi/gst-editing-services,volodymyrrudyi/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,cfoch/ges,cfoch/ges,pitivi/gst-editing-services,volodymyrrudyi/gst-editing-services,pitivi/gst-editing-services,cfoch/gst-editing-services,volodymyrrudyi/gst-editing-services