remove `YYDispatchQueuePool` due to dynamic library compile error.

YYCache/YYMemoryCache.m

@@ -15,19 +15,10 @@
 #import <QuartzCore/QuartzCore.h>
 #import <pthread.h>
 
-#if __has_include("YYDispatchQueuePool.h")
-#import "YYDispatchQueuePool.h"
-#endif
 
-#ifdef YYDispatchQueuePool_h
-static inline dispatch_queue_t YYMemoryCacheGetReleaseQueue() {
-    return YYDispatchQueueGetForQOS(NSQualityOfServiceUtility);
-}
-#else
 static inline dispatch_queue_t YYMemoryCacheGetReleaseQueue() {
     return dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
 }
-#endif
 
 /**
  A node in linked map.