Don't output beatmap parse failures in a visible manner

The user can't do much about this. When a user reports a beatmap issue,
the logs will still contain this useful information. Should be fine I
think.

As mentioned in

https://github.com/ppy/osu/discussions/18426
https://github.com/ppy/osu/issues/750
https://github.com/ppy/osu/issues/18372

etc.

osu.Game/Beatmaps/Formats/LegacyDecoder.cs

@@ -59,7 +59,7 @@ namespace osu.Game.Beatmaps.Formats
                 }
                 catch (Exception e)
                 {
-                    Logger.Log($"Failed to process line \"{line}\" into \"{output}\": {e.Message}", LoggingTarget.Runtime, LogLevel.Important);
+                    Logger.Log($"Failed to process line \"{line}\" into \"{output}\": {e.Message}");
                 }
             }
         }