Delete dysfunctional fork_revert feature (#8891)

I found myself having to update this code for Gloas, and figured we may as well delete it seeing as it doesn't work.

See:

- https://github.com/sigp/lighthouse/issues/4198


  Delete all `fork_revert` logic and the accompanying test.


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

beacon_node/store/src/iter.rs

@@ -249,7 +249,6 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> Iterator
 pub struct ParentRootBlockIterator<'a, E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> {
     store: &'a HotColdDB<E, Hot, Cold>,
     next_block_root: Hash256,
-    decode_any_variant: bool,
     _phantom: PhantomData<E>,
 }
 
@@ -260,17 +259,6 @@ impl<'a, E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>
         Self {
             store,
             next_block_root: start_block_root,
-            decode_any_variant: false,
-            _phantom: PhantomData,
-        }
-    }
-
-    /// Block iterator that is tolerant of blocks that have the wrong fork for their slot.
-    pub fn fork_tolerant(store: &'a HotColdDB<E, Hot, Cold>, start_block_root: Hash256) -> Self {
-        Self {
-            store,
-            next_block_root: start_block_root,
-            decode_any_variant: true,
             _phantom: PhantomData,
         }
     }
@@ -285,12 +273,10 @@ impl<'a, E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>>
             Ok(None)
         } else {
             let block_root = self.next_block_root;
-            let block = if self.decode_any_variant {
-                self.store.get_block_any_variant(&block_root)
-            } else {
-                self.store.get_blinded_block(&block_root)
-            }?
-            .ok_or(Error::BlockNotFound(block_root))?;
+            let block = self
+                .store
+                .get_blinded_block(&block_root)?
+                .ok_or(Error::BlockNotFound(block_root))?;
             self.next_block_root = block.message().parent_root();
             Ok(Some((block_root, block)))
         }