[sleep_strategy/Stats] remove old obsolete stats member

Before 713c0f04 emper::sleep_strategy::Stats had the actual stats member but with 713c0f04 WorkerStats are introduced which have the actual stats member but I apparently forgot to remove the old now obsolete members.

Thanks clang for detecting this!
See: https://gitlab.cs.fau.de/aj46ezos/emper/-/jobs/456981

emper/sleep_strategy/Stats.hpp

@@ -34,15 +34,6 @@ namespace emper::sleep_strategy {
 class Stats;
 
 class Stats {
-	friend class PipeSleepStrategy;
-
-	size_t onNewWork = 0;
-	size_t notify = 0;
-	size_t notifications = 0;
-	size_t skip = 0;
-	size_t wakeup = 0;
-	size_t wakeupDueToNotify = 0;
-
 	WorkerStats anywhereStats;
 	std::mutex anywhereStatsMutex;