deinterlace: remove check for impossible condition

Commit bd27a1f3 added a few error handling
memory management checks. These check srccaps to see if it needs to be
unreferenced before returning, in the case of invalid_caps this goto jump
always happens before srccaps is set, so it will always be NULL in this
error label.

CID #1352035

gst/deinterlace/gstdeinterlace.c

@@ -2692,8 +2692,6 @@ gst_deinterlace_setcaps (GstDeinterlace * self, GstPad * pad, GstCaps * caps)
 invalid_caps:
   {
     GST_ERROR_OBJECT (pad, "Invalid caps: %" GST_PTR_FORMAT, caps);
-    if (srccaps)
-      gst_caps_unref (srccaps);
     return FALSE;
   }
 set_caps_failed: