1. Based on the principle not to break the mongo build, in WT-16803 we were focusing on introduce version based parameter only. The purpose for this ticket is based on the context that as there's no reference to pl_complete_checkpoint, we have no reason to keep using pl_complete_checkpoint_ext any more, and both the pali side and wt side should deprecate this function.

Before merging the PR, make sure server side can work well (regardless the commit sequence) with the new commit. If we cannot guarantee that PRs from both side cannot be made at the same time, then a potential approach can be use double commit with following steps:

• The PALI side commit the change to set the value to complete, and complete_ext = NULL, makes it works well before WT drop.
  • Please be very careful that current implementation in mongo repo does not guarantee pl_complete_checkpoint is either NULL or valid function pointer, so use != NULL is not enough to check whether PALI side is changed.
• Commit the first action for a check if checkpoint_complete is not NULL then call it otherwise call ext.
• PALI side then remove the NULL pointer set to pl_complete_checkpoint_ext and then submit the PR
• Commit the second action to remove _ext then merge it.
• Done.

Though it's complex but the point is to avoid a continuous CI failure in mongo waterfall.