Originally checkpoint is checking for xid, however, xid is used to control the
transaction visibility and it's crucial to clean this xid if process is done
with commit and before release locks.

However, checkpoint need to wait for the `AtExat_smgr()` to cleanup persistent
table information, which happened after release locks, where `xid` is already
cleaned.

Hence, we use VXID, which doesn't have visibility impact.

NOTE: Upstream PostgreSQL commit f21bb9cf for the
similar fix.