Don't store code tree structures in tests

[IndrajeetPatil]

Closes #1206

And also remove everything that was needed for R 3.2.

Script used to delete files:

tree_files_to_delete <-
  fs::dir_ls(
    path = ".",
    glob = "*.R|*.Rprofile|*.Rmd|*.Rmarkdown|*.Rnw|*.Qmd",
    invert = TRUE,
    type = "file",
    recurse = TRUE
  ) |>
  stringr::str_subset("_tree") |>
  purrr::map_chr(fs::path_abs)

stopifnot(all(fs::file_exists(tree_files_to_delete)))

fs::file_delete(tree_files_to_delete)

[github-actions[bot]]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 4f782529e2419471d9abcf60899bf28a34bd5268 is merged into main:

• :heavy_check_mark:cache_applying: 163ms -> 161ms [-3.76%, +0.93%]
• :exclamation::snail:cache_recording: 526ms -> 529ms [+0.02%, +1.14%]
• :heavy_check_mark:without_cache: 992ms -> 995ms [-0.17%, +0.72%]

Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions[bot]]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 4f782529e2419471d9abcf60899bf28a34bd5268 is merged into main:

• :heavy_check_mark:cache_applying: 161ms -> 161ms [-2.78%, +2.16%]
• :heavy_check_mark:cache_recording: 526ms -> 527ms [-0.74%, +1.24%]
• :heavy_check_mark:without_cache: 987ms -> 988ms [-0.38%, +0.58%]

Further explanation regarding interpretation and methodology can be found in the documentation.