vo_gpu: suppress PL_FATAL logs during probing

These were still mapped to MP errors during probing, but they also get
triggered when instance creation fails due to lack of support for e.g.
wayland. Since waylandvk is probed above x11vk, we should probably
suppress these by default.

Closes #7626

video/out/placebo/utils.c

@@ -27,8 +27,6 @@ static const enum pl_log_level probing_map(enum pl_log_level level)
 {
     switch (level) {
     case PL_LOG_FATAL:
-        return PL_LOG_ERR;
-
     case PL_LOG_ERR:
     case PL_LOG_WARN:
         return PL_LOG_INFO;