Summary
Remove the following check in __rec_fill_tw_from_upd_select.c and turn that into an assert as it should not happen.

         *
         * FIXME-WT-6557: no need to check this after WT-6557 is done as the tombstone will be freed
         * when it is written to the disk image in the previous eviction.
         */
        if (!F_ISSET(tombstone, WT_UPDATE_RESTORED_FROM_DS | WT_UPDATE_RESTORED_FROM_HS)) {
            WT_RET(__rec_append_orig_value(session, page, tombstone, vpack));

Motivation

• Does this affect any team outside of WT?
  (Are they blocked? Are they waiting for an answer?)
  No

• How likely is it that this use case or problem will occur?
  (Main path? Edge case? Frequency of the issue?)
  N/A

• If the problem does occur, what are the consequences and how severe are they?
  (A minor annoyance at a log message? Performance concern? Outage/unavailability? Test Failure?)

• Is this issue urgent?
  (Does this ticket have a required timeline? What is it?)
  No

Acceptance Criteria (Definition of Done)
(When will this ticket be considered done? What is the acceptance criteria for this ticket to be closed?)

• Testing
  (What all testing needs to be done as part of this ticket? Unit? Functional? Performance?Testing at MongoDB side?)

• Documentation update
  (Does this ticket require a change in the architecture guide? If yes, please create a corresponding doc ticket.)

[Optional] Suggested Solution
(Is there any suggested solution to handle this issue? Is it related to any existing WT ticket? Is it related to any previous issue fixed? If yes, link the WT ticket number using related to, depends on, dependent on by links)
Turn the check into an assert