video-aggregator: Fix renegotiation when using convert pads

Since 23189c60 we started using the
useless result of `modified_caps` which, was never used since it was
introduced 7 years ago (in videomixer2). The intersection is useless and
we should just avoid doing it at all (which was always the case before)
as it can end up failing renegotiation for bad reasons.

Part-of: <gstreamer/gst-plugins-base!905>

gst-libs/gst/video/gstvideoaggregator.c

@@ -2491,10 +2491,7 @@ gst_video_aggregator_pad_sink_acceptcaps (GstPad * pad,
     GstVideoAggregator * vagg, GstCaps * caps)
 {
   gboolean ret;
-  GstCaps *modified_caps;
   GstCaps *accepted_caps;
-  GstCaps *template_caps;
-  gboolean had_current_caps = TRUE;
   gint i, n;
   GstStructure *s;
   GstAggregator *agg = GST_AGGREGATOR (vagg);
@@ -2503,12 +2500,8 @@ gst_video_aggregator_pad_sink_acceptcaps (GstPad * pad,
 
   accepted_caps = gst_pad_get_current_caps (GST_PAD (agg->srcpad));
 
-  template_caps = gst_pad_get_pad_template_caps (GST_PAD (agg->srcpad));
-
-  if (accepted_caps == NULL) {
-    accepted_caps = template_caps;
-    had_current_caps = FALSE;
-  }
+  if (accepted_caps == NULL)
+    accepted_caps = gst_pad_get_pad_template_caps (GST_PAD (agg->srcpad));
 
   accepted_caps = gst_caps_make_writable (accepted_caps);
 
@@ -2528,15 +2521,10 @@ gst_video_aggregator_pad_sink_acceptcaps (GstPad * pad,
     }
   }
 
-  modified_caps = gst_caps_intersect (accepted_caps, template_caps);
-
-  ret = gst_caps_can_intersect (caps, modified_caps);
+  ret = gst_caps_can_intersect (caps, accepted_caps);
   GST_DEBUG_OBJECT (pad, "%saccepted caps %" GST_PTR_FORMAT,
       (ret ? "" : "not "), caps);
   gst_caps_unref (accepted_caps);
-  gst_caps_unref (modified_caps);
-  if (had_current_caps)
-    gst_caps_unref (template_caps);
   return ret;
 }