Remove unnecessary set_index to fix stat module for function-taxonomy analysis

[reid-wagner]

Removes unncessary set_index call. The 'id' column does not exist for function-taxonomy analysis (mode='ft') input, from the filter or expand modules, causing the error below. Comments state this was included for testing, and removing it does not affect output results.

Also, make a small correction to comments.

  File "/usr/local/lib/python3.14/site-packages/metaquantome/modules/stat.py", line 53, in stat
    df_tmp = test_norm_intensity(df, tmp_samp_grps, paired, parametric)
  File "/usr/local/lib/python3.14/site-packages/metaquantome/modules/stat.py", line 123, in test_norm_intensity
    df_means.set_index('id', drop=False, inplace=True)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.14/site-packages/pandas/core/frame.py", line 6977, in set_index
    raise KeyError(f"None of {missing} are in the columns")
KeyError: "None of ['id'] are in the columns"