trim_data: Dummy function to conduct no trimming at all.
In kaz-yos/trim3: Conduct Three-Group Trimming Study

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1 2	trim_data(data, trim_method_name, thres, A_name, ps0_name, ps1_name, ps2_name, levels)

`data`	data_frame
`trim_method_name`	Function used for trimming that takes `A`, `ps0`, `ps1`, `ps2`, `levels`, and `thres` as arguments. Either one of the string: `none`, `crump`, `sturmer`, `walker`.
`thres`	Threshold for the trimming strategy.
`A_name`	Treatment indicator name in `data`.
`ps0_name`	Name of the column in `data` for the PS for the first level.
`ps1_name`	Name of the column in `data` for the PS for the second level.
`ps2_name`	Name of the column in `data` for the PS for the third level.
`levels`	Character vector holding three elements corresponding to levels in `A`