Remove source info from log messages

slog.HandlerOptions.AddSource is a cool feature, but since we moved the
logger to a separate package it no longer works. It now always shows
source info for the log package, rather than the code that called it.

This change removes it.

internal/logging/logging.go

@@ -29,9 +29,7 @@ func Init() {
 
 	logger = Logger{
 		slog.New(
-			slog.NewJSONHandler(lj, &slog.HandlerOptions{
-				AddSource: cfg.LogAddSource,
-			}),
+			slog.NewJSONHandler(lj, &slog.HandlerOptions{}),
 		),
 	}
 }