Gracefully handle deleting states prior to anchor_slot (#8409)

Fix an issue detected by @jimmygchen that occurs when checkpoint sync is aborted midway and then later restarted.

The characteristic error is something like:

> Nov 13 00:51:35.832 ERROR Database write failed                         error: Hdiff(LessThanStart(Slot(1728288), Slot(1728320))), action: "reverting blob DB changes"
Nov 13 00:51:35.833 WARN  Hot DB pruning failed                         error: DBError(HotColdDBError(Rollback))

This issue has existed since v7.1.0.


  Delete snapshot/diff in the case where `hot_storage_strategy` fails.


Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

Author: michaelsproul

beacon_node/store/src/hot_cold_store.rs

@@ -1308,8 +1308,13 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
                         state_root.as_slice().to_vec(),
                     ));
 
-                    if let Some(slot) = slot {
-                        match self.hot_storage_strategy(slot)? {
+                    // NOTE: `hot_storage_strategy` can error if there are states in the database
+                    // prior to the `anchor_slot`. This can happen if checkpoint sync has been
+                    // botched and left some states in the database prior to completing.
+                    if let Some(slot) = slot
+                        && let Ok(strategy) = self.hot_storage_strategy(slot)
+                    {
+                        match strategy {
                             StorageStrategy::Snapshot => {
                                 // Full state stored in this position
                                 key_value_batch.push(KeyValueStoreOp::DeleteKey(