chore: stop naming mode in indexing.R

[maelle]

One of those was unused. It seemed clearer not to name any?

[maelle]

Hide white space in the diff otherwise it's not helpful 😺

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 7db27b0 is merged into main:

• ✔️as_adjacency_matrix: 850ms -> 853ms [-1.14%, +1.81%]
• ✔️as_biadjacency_matrix: 807ms -> 808ms [-1.83%, +2.18%]
• ✔️as_data_frame_both: 1.63ms -> 1.65ms [-1.43%, +3.9%]
• ✔️as_long_data_frame: 4.11ms -> 4.15ms [-3.97%, +6%]
• ✔️es_attr_filter: 2.92ms -> 2.94ms [-2.89%, +4.27%]
• ✔️graph_from_adjacency_matrix: 155ms -> 154ms [-2.54%, +0.61%]
• ✔️graph_from_data_frame: 3.57ms -> 3.6ms [-1.16%, +2.56%]
• ✔️vs_attr_filter: 1.69ms -> 1.64ms [-7.19%, +1.51%]
• ✔️vs_by_name: 1.17ms -> 1.14ms [-6.81%, +2.41%]
  Further explanation regarding interpretation and methodology can be found in the documentation.