[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.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #2155 from chenghao-intel/treenode and squashes the following commits:

7cf2cd2 [Cheng Hao] Remove the implicit keyword for TreeNodeRef and some other small issues
5873415 [Cheng Hao] Remove the TreeNode.id