tests: integration: Remove the effect in test_seeking
tests: integration: Remove the effect in test_seeking

It complexifies the test but this is not what we actually want in
that test

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