message: simplify: Remove redundant edge collapse candidates
  When considering an edge v0-v1, one of the collapse directions is more
  optimal so we can just pick that one based on the error.
  This makes simplifying large meshes ~2x faster.
diff: @@ -163,10 +163,9 @@ namespace
  unsigned int i1 = indices[i + next[e]];
  Collapse c01 = { i0, i1, quadricError(vertex_quadrics[i0], vertex_positions[i1]) };
  - edge_collapses.push_back(c01);
  -
  Collapse c10 = { i1, i0, quadricError(vertex_quadrics[i1], vertex_positions[i0]) };
  - edge_collapses.push_back(c10);
  +
  + edge_collapses.push_back(c01.error <= c10.error ? c01 : c10);
  }
  }
  