Don't compute the unused ephemeral nodes (#2579)

storage/cache/log_tile.go

@@ -83,10 +83,6 @@ func PopulateLogTile(st *storagepb.SubtreeProto, hasher hashers.LogHasher) error
 			return err
 		}
 	}
-	_, err := cr.GetRootHash(store)
-	if err != nil {
-		return fmt.Errorf("failed to compute root hash: %v", err)
-	}
 
 	// Additional check - after population we should have the same number of internal nodes
 	// as before the subtree was written to storage. Either because they were loaded from

storage/mysql/storage_test.go

@@ -177,10 +177,6 @@ func createLogNodesForTreeAtSize(t *testing.T, ts, rev int64) ([]stree.Node, err
 			return nil, err
 		}
 	}
-	// Store the ephemeral nodes as well.
-	if _, err := cr.GetRootHash(store); err != nil {
-		return nil, err
-	}
 
 	// Unroll the map, which has deduped the updates for us and retained the latest
 	nodes := make([]stree.Node, 0, len(nodeMap))

storage/testonly/fake_node_reader.go

@@ -126,7 +126,7 @@ func NewMultiFakeNodeReaderFromLeaves(batches []LeafBatch) *MultiFakeNodeReader
 			}
 		}
 		// TODO(pavelkalinnikov): Use testing.T.Fatalf instead of panics.
-		root, err := cr.GetRootHash(store) // Store the ephemeral nodes as well.
+		root, err := cr.GetRootHash(nil)
 		if err != nil {
 			panic(fmt.Errorf("GetRootHash: %v", err))
 		}