maint: Remove redundant private functions from pkg/private. * pkg/private/rstrip.m: remove file * pkg/private/strip.m: remove file * pkg/private/split_by.m: remove file * pkg/private/get_description.m: replace rstrip with deblank and strip with strtrim * pkg/private/fix_depends.m: replace rstrip with deblanak, strip with strtrim and split_by with strstrip (strsplit ()) * pkg/private/generate_llokfor_cache.m: replace split_by with strsplit (strtrim ())