Remove NormalizedNodePruner.SimpleStack

Remove NormalizedNodePruner.SimpleStack

This custom implementation is highly inefficient, because:
1) peek/pop operations perform get(int) and remove(int) operations
   on ArrayList, which are highly inefficient O(N)
2) it allocates an object for each entry

Replace this class with a stock Deque, which takes care of the first
problem, as push/pop/peek are amortized O(1).

For implementation use an ArrayDeque, which takes care of the second
problem, as stack entries are reused.

Change-Id: Ie59e2fb47f841e4e5fc08c3ab7e164ad0cb368ad
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>