[SPARK-3198] [SQL] Remove the TreeNode.id

Thus id property of the TreeNode API does save time in a faster way to compare 2 TreeNodes, it is kind of performance bottleneck during the expression object creation in a multi-threading env (because of the memory barrier). 
Fortunately, the tree node comparison only happen once in master, so even we remove it, the entire performance will not be affected.
Add back in an `eq` check to avoid the expensive equality checking when the same object is returned.