Revert replacement of @synchronized in SDWebImageCombinedOperation

SDWebImage/SDWebImageManager.m

@@ -347,34 +347,20 @@
 @end
 
 
-@interface SDWebImageCombinedOperation ()
-
-@property (strong, nonatomic, nonnull) dispatch_semaphore_t cancelLock; // a lock to make the `cancel` method thread-safe
-
-@end
-
 @implementation SDWebImageCombinedOperation
 
-- (instancetype)init {
-    self = [super init];
-    if (self) {
-        _cancelLock = dispatch_semaphore_create(1);
-    }
-    return self;
-}
-
 - (void)cancel {
-    LOCK(self.cancelLock);
-    self.cancelled = YES;
-    if (self.cacheOperation) {
-        [self.cacheOperation cancel];
-        self.cacheOperation = nil;
+    @synchronized(self) {
+        self.cancelled = YES;
+        if (self.cacheOperation) {
+            [self.cacheOperation cancel];
+            self.cacheOperation = nil;
+        }
+        if (self.downloadToken) {
+            [self.manager.imageDownloader cancel:self.downloadToken];
+        }
+        [self.manager safelyRemoveOperationFromRunning:self];
     }
-    if (self.downloadToken) {
-        [self.manager.imageDownloader cancel:self.downloadToken];
-    }
-    [self.manager safelyRemoveOperationFromRunning:self];
-    UNLOCK(self.cancelLock);
 }
 
 @end