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