protected CacheEntry getCacheEntry(ICachedMNode node) {
    return node.getCacheEntry();
  }
Unpin a node, and if the lock mayer on this node is zero, it will be evictable. Unpin a node
means decrease one mayer lock from the node. If the lock mayer reaches zero, the mayer lock of
its parent should decrease.

@param node
@return
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/memory/MemoryManager.java