message: [pdsl_core] Slightly refactor HashMap probing
  Also remove some debug artifacts from the code.
diff: @@ -110,7 +110,7 @@ impl<K, V> HashMap<K, V> {
  /// Converts the given bytes into a `u32` value.
  ///
  /// The first byte in the array will be the most significant byte.
  -fn bytes_to_u32(bytes: [u8; 4]) -> u32 {
  +fn bytes4_to_u32(bytes: [u8; 4]) -> u32 {
  let mut res = 0;
  res |= (bytes[0] as u32) << 24;
  res |= (bytes[1] as u32) << 16;
  @@ -208,7 +208,7 @@ where
  {
  // Convert the first 4 bytes in the keccak256 hash
  // of the key into a big-endian unsigned integer.
  - let probe_start = bytes_to_u32(
  + let probe_start = bytes4_to_u32(
  slice_as_array4(
  &(hash::keccak256(key.borrow())[0..4])
  ).expect(
  @@ -219,14 +219,8 @@ where
  // This is the offset for the quadratic probing.
  let mut probe_hops = 0;
  let mut probe_offset = 0;
  - use std::collections::HashSet;
  - let mut probed_set = HashSet::<u32>::new();
  - 'outer: loop {
  - if probe_hops == Self::MAX_PROBE_HOPS {
  - return None
  - }
  + 'outer: while probe_hops < Self::MAX_PROBE_HOPS {
  let probe_index = probe_start.wrapping_add(probe_offset);
  - probed_set.insert(probe_index);
  match self.entries.get(probe_index).unwrap() {
  Some(Entry::Occupied(entry)) => {
  if key == entry.key.borrow() {
  @@ -254,6 +248,7 @@ where
  }
  }
  }
  + None
  }
  /// Probes for a free or usable slot while inserting.
  