src: delete unreachable code in node_perf.h

Signed-off-by: gengjiawen <technicalcute@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/25850
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_perf.h

@@ -34,7 +34,6 @@ static inline const char* GetPerformanceMilestoneName(
 #undef V
     default:
       UNREACHABLE();
-      return 0;
   }
 }