aux/trace: stop dumping transfer data for threaded contexts

this is only useful for unit testing (and is it really useful even then?),
and does nothing but explode trace dumps and demolish performance otherwise

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10899>

src/gallium/auxiliary/driver_trace/tr_context.c

@@ -1634,7 +1634,7 @@ trace_context_transfer_unmap(struct pipe_context *_context,
 
    trace_dump_call_end();
 
-   if (tr_trans->map) {
+   if (tr_trans->map && !tr_ctx->threaded) {
       /*
        * Fake a texture/buffer_subdata
        */