Revert "fix checkpoint block potentially not getting backfilled into DB"

[tersec]

Reverts #5863

Will wait a small amount of time to see if one of the previous commits marks where this begins.

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Unsupported **size** in type/size combination: array[0,uint8]
Unsupported **size** in type/size combination: array[0,uint128]
Unsupported **size** in type/size combination: array[0,bool]
Unsupported **size** in type/size combination: array[0,uint64]
s.. (0.05s)
Slashing Interchange tests  [Preset: mainnet] ..s...s.....................s......... (0.43s)
Slashing Protection DB [Preset: mainnet] ............ (0.15s)
Validator Client test suite ........... (1.55s)
Block pool processing [Preset: mainnet] ..... (0.54s)
Block pool altair processing [Preset: mainnet] . (0.37s)
chain DAG finalization tests [Preset: mainnet] .... (2.90s)
Old database versions [Preset: mainnet] . (0.06s)
Diverging hardforks .. (0.27s)
Backfill .... (0.89s)
Starting states F (0.10s)
============================
  build/all_tests 'Starting states::Starting state without block'
----------------------------
    tests/test_blockchain_dag.nim(1157, 45): Check failed: dag.getBlockIdAtSlot(dag.tail.slot - 2).isNone

  [FAILED ] (  0.10s) Starting state without block

(0.10s)   Starting states

Latest valid hash [Preset: mainnet] . (1.06s)
Pruning . (4.23s)
State history . (0.21s)
Ancestry . (0.43s)

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one down, one to go

[tersec]

Reverting.

This is basically the interaction between #5863 and #5869 of which the latter happened to merge to unstable first. Both individually passed CI fine.