Fix debug build failure (#4774)

cugraph is no longer dependent on cugraph_ops and no longer pulls files from the cugrpahops repo. But we have two `assert` statements still assuming cugrpahops files are available. These assert statements are compiled only in the debug mode. This PR fixes build errors due to these assert statements in the debug build.

Closes #4763

Authors:
  - Seunghwa Kang (https://github.com/seunghwak)
  - Chuck Hastings (https://github.com/ChuckHastings)

Approvers:
  - Chuck Hastings (https://github.com/ChuckHastings)
  - Joseph Nke (https://github.com/jnke2016)

URL: #4774

cpp/src/prims/detail/sample_and_compute_local_nbr_indices.cuh

@@ -597,8 +597,6 @@ rmm::device_uvector<edge_t> compute_uniform_sampling_index_without_replacement(
   raft::random::RngState& rng_state,
   size_t K)
 {
-  assert(cugraph::invalid_edge_id_v<edge_t> == cugraph::ops::graph::INVALID_ID<edge_t>);
-
   edge_t mid_partition_degree_range_last = static_cast<edge_t>(K * 10);  // tuning parameter
   assert(mid_partition_degree_range_last > K);
   size_t high_partition_oversampling_K = K * 2;  // tuning parameter
@@ -1567,10 +1565,7 @@ uniform_sample_and_compute_local_nbr_indices(
   size_t K,
   bool with_replacement)
 {
-  using edge_t = typename GraphViewType::edge_type;
-
-  assert(cugraph::invalid_edge_id_v<edge_t> == cugraph::ops::graph::INVALID_ID<edge_t>);
-
+  using edge_t   = typename GraphViewType::edge_type;
   using vertex_t = typename GraphViewType::vertex_type;
   using key_t    = typename thrust::iterator_traits<KeyIterator>::value_type;
 

cpp/src/sampling/neighbor_sampling_impl.hpp

@@ -179,7 +179,7 @@ neighbor_sample_impl(raft::handle_t const& handle,
                     ? (fan_out.size() / num_edge_types)
                     : ((fan_out.size() / num_edge_types) + 1);
 
-  for (auto hop = 0; hop < num_hops; hop++) {
+  for (size_t hop = 0; hop < num_hops; ++hop) {
     for (auto edge_type_id = 0; edge_type_id < num_edge_types; edge_type_id++) {
       auto k_level = fan_out[(hop * num_edge_types) + edge_type_id];
       rmm::device_uvector<vertex_t> srcs(0, handle.get_stream());