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.h

@@ -32,8 +32,7 @@ AS_SUBCLASSING_RESTRICTED
  *
  * @discussion You may pass @c nil for the handler if you simply want the objects to
  * be retained at enqueue time, and released during the run loop step. This is useful
- * for creating a "main deallocation queue", as @c ASDeallocQueue creates its own 
- * worker thread with its own run loop.
+ * for creating a "main deallocation queue".
  */
 - (instancetype)initWithRunLoop:(CFRunLoopRef)runloop
                   retainObjects:(BOOL)retainsObjects
@@ -78,14 +77,4 @@ NS_INLINE ASCATransactionQueue *ASCATransactionQueueGet(void) {
   return _ASSharedCATransactionQueue;
 }
 
-@interface ASDeallocQueue : NSObject
-
-+ (ASDeallocQueue *)sharedDeallocationQueue NS_RETURNS_RETAINED;
-
-- (void)drain;
-
-- (void)releaseObjectInBackground:(id __strong _Nullable * _Nonnull)objectPtr;
-
-@end
-
 NS_ASSUME_NONNULL_END