CLI should remove empty folder when removing a field

[jaybythebay]

I'm not positive we want to change this behavior. Perhaps we'd just want a separate clean_folders command to remove empty folders

Add a folder:

tableau_utilities --clean_dir --location local --file_path '/Users/jayrosenthal/Downloads/test.tdsx' --save_tds datasource --column_name MY_COLUMN --folder_name 'My New Folder'

Move that single column back out of a folder

tableau_utilities --clean_dir --location local --file_path '/Users/jayrosenthal/Downloads/test.tdsx' --save_tds datasource --column_name MY_COLUMN --folder_name 'Original Folder'

'My New Folder' is still in the file which adds clutter.