gstreamer/log: Fix debug_remove_default_log_function() to actually work

We have to pass `NULL` / `None` instead of the actual default log
function as because of `-Bsymbolic` or how DLLs work on Windows the
external function pointer is different to the internal one.

gstreamer/src/log.rs

@@ -382,7 +382,7 @@ where
 pub fn debug_remove_default_log_function() {
     skip_assert_initialized!();
     unsafe {
-        gst_sys::gst_debug_remove_log_function(Some(gst_sys::gst_debug_log_default));
+        gst_sys::gst_debug_remove_log_function(None);
     }
 }