refactor remove function

- use one awk command instead of two, to determine if package is not removable
- save comparison files to /etc/setup instead of /tmp
- save as "essential.lst" and "$pkg.lst" respectively
- use warnings where appropriate
- new file list logic
  - extract file list
  - if package is essential, remove file list and exit
  - if package is not essential, remove package, remove file list and continue
- new delete logic
  - remove all files
  - remove empty directories
- utilize awk inplace where appropriate