libs: encoder: don't unref properties

This patch fixes a regression introduced in commit 148f867c, since the
props variable is set to object's member variable
encoder->properties. And it is set in the instance initialization,
thus it will not be leaked.

https://bugzilla.gnome.org/show_bug.cgi?id=787733

gst-libs/gst/vaapi/gstvaapiencoder.c

@@ -1264,7 +1264,6 @@ gst_vaapi_encoder_init_properties (GstVaapiEncoder * encoder)
       return FALSE;
   }
 
-  g_ptr_array_unref (props);
   return TRUE;
 }