Remove background deallocation helper code (#1890)

* Remove background deallocation helper code

Last use removed in Texture with #1840, now PINS no longer uses it either. Less OOMs is so nice.

* remove methods from docs

Source/ASRunLoopQueue.mm

@@ -27,67 +27,6 @@ static void runLoopSourceCallback(void *info) {
 #endif
 }
 
-#pragma mark - ASDeallocQueue
-
-@implementation ASDeallocQueue {
-  std::vector<CFTypeRef> _queue;
-  AS::Mutex _lock;
-}
-
-+ (ASDeallocQueue *)sharedDeallocationQueue NS_RETURNS_RETAINED
-{
-  static ASDeallocQueue *deallocQueue = nil;
-  static dispatch_once_t onceToken;
-  dispatch_once(&onceToken, ^{
-    deallocQueue = [[ASDeallocQueue alloc] init];
-  });
-  return deallocQueue;
-}
-
-- (void)dealloc
-{
-  ASDisplayNodeFailAssert(@"Singleton should not dealloc.");
-}
-
-- (void)releaseObjectInBackground:(id  _Nullable __strong *)objectPtr
-{
-  NSParameterAssert(objectPtr != NULL);
-  
-  // Cast to CFType so we can manipulate retain count manually.
-  const auto cfPtr = (CFTypeRef *)(void *)objectPtr;
-  if (!cfPtr || !*cfPtr) {
-    return;
-  }
-  
-  _lock.lock();
-  const auto isFirstEntry = _queue.empty();
-  // Push the pointer into our queue and clear their pointer.
-  // This "steals" the +1 from ARC and nils their pointer so they can't
-  // access or release the object.
-  _queue.push_back(*cfPtr);
-  *cfPtr = NULL;
-  _lock.unlock();
-  
-  if (isFirstEntry) {
-    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.100 * NSEC_PER_SEC)), dispatch_get_global_queue(QOS_CLASS_DEFAULT, 0), ^{
-      [self drain];
-    });
-  }
-}
-
-- (void)drain
-{
-  _lock.lock();
-  const auto q = std::move(_queue);
-  _lock.unlock();
-  for (CFTypeRef ref : q) {
-    // NOTE: Could check that retain count is 1 and retry later if not.
-    CFRelease(ref);
-  }
-}
-
-@end
-
 @implementation ASAbstractRunLoopQueue
 
 - (instancetype)init