depend-cleanup.sh: Generalise lib32 code and avoid duplication

By passing through _ALL_libcompats we can avoid hard-coding the list of
libcompats in depend-cleanup.sh. This cleanup also makes clean_dep
shorter by using a loop instead of handling each case explicitly (at the
expense of slightly tweaked logging).

Reviewed by: brooks, jhb
Differential Revision: https://reviews.freebsd.org/D41187

(cherry picked from commit 81805ec30074363e5d7d7add37b3ccf4f1eb396b)

Pull Request: https://github.com/freebsd/freebsd-src/pull/1543