Remove histograms

Rumor has it these are very expensive to compute, so let's remove them
for now.

firewood/src/merkle.rs

@@ -416,9 +416,6 @@ impl<S: ReadableStorage> Merkle<NodeStore<MutableProposal, S>> {
     /// Map `key` to `value` in the trie.
     /// Each element of key is 2 nibbles.
     pub fn insert(&mut self, key: &[u8], value: Box<[u8]>) -> Result<(), MerkleError> {
-        histogram!("firewood.insert.key.length").record(key.len() as f64);
-        histogram!("firewood.insert.data.length").record(value.len() as f64);
-
         let key = Path::from_nibbles_iterator(NibblesIterator::new(key));
 
         let root = self.nodestore.mut_root();

storage/src/nodestore.rs

@@ -492,7 +492,6 @@ impl<S: ReadableStorage> NodeStore<Arc<ImmutableProposal>, S> {
     /// Also returns the index of the free list the node was allocated from.
     pub fn allocate_node(&mut self, node: &Node) -> Result<(LinearAddress, AreaIndex), Error> {
         let stored_area_size = Self::stored_len(node);
-        histogram!("firewood.node_size").record(stored_area_size as f64);
 
         // Attempt to allocate from a free list.
         // If we can't allocate from a free list, allocate past the existing