Remove R code that are no longer needed

[GaryBAYLOR]

To improve code readability, it is better to remove the R code that is no longer needed, instead of commenting out but retaining each line. The historical code can be easily tracked in the commit histories in Github.

For example,

In CVtreeMLE.R line 408-411,

      # mixed_comb_results <- est_comb_mixture_rules(At, Av, W, Y, rules, no_mix_rules, Q1_stack)

      # fold_results_mix_combo_data[[fold_k]] <- mixed_comb_results$data
      # fold_results_mix_Sls[[fold_k]] <- mixed_comb_results$learner

      results_list <- list(
        fold_results_mix_rules,
        mix_fold_data,
        mix_fold_directions,
        fold_results_marg_rules,
        fold_results_marg_directions,
        fold_results_marginal_data,
        # fold_results_marginal_additive_data,
        fold_results_marginal_combo_data,
        fold_results_marginal_Sls
        # fold_results_mix_combo_data,
        # fold_results_mix_Sls
      )

can be reduced to

      results_list <- list(
        fold_results_mix_rules,
        mix_fold_data,
        mix_fold_directions,
        fold_results_marg_rules,
        fold_results_marg_directions,
        fold_results_marginal_data,
        fold_results_marginal_combo_data,
        fold_results_marginal_Sls
      )

The same applies to other parts of the function and other functions.

[blind-contours]

I've done a massive editing and via linting identified and removed all these areas.