Revert "LedgerDB.V2: make in-memory LedgerTablesHandle.close a no-op"

This reverts commit 7900088.

Without the fix in the preceding commit, this would cause test failures, see

    cabal run ouroboros-consensus-diffusion:mock-test -- \
      --quickcheck-replay="(SMGen 15972426649573867634 4412022096428701771,88)" \
      -p '/Praos.simple convergence/'

Author: amesgen

ouroboros-consensus/src/ouroboros-consensus/Ouroboros/Consensus/Storage/LedgerDB/V2/InMemory.hs

@@ -96,11 +96,7 @@ newInMemoryLedgerTablesHandle tracer someFS@(SomeHasFS hasFS) l = do
   pure
     LedgerTablesHandle
       { close = do
-          -- Temporarily a no-op until
-          -- https://github.com/IntersectMBO/ouroboros-consensus/issues/1551 has
-          -- been fixed.
-
-          -- atomically $ writeTVar tv LedgerTablesHandleClosed
+          atomically $ writeTVar tv LedgerTablesHandleClosed
           traceWith tracer V2.TraceLedgerTablesHandleClose
       , duplicate = do
           hs <- readTVarIO tv