readutmp: simplify extract_trimmed_name via ximemdup0 * lib/readutmp.c (extract_trimmed_name): Simplify. * modules/readutmp (Depends-on): Add strnlen, which was a missing dependency. * lib/readutmp.c: Include xmemdup0. (extract_trimmed_name): Simplify. * modules/readutmp (Depends-on): Add xmemdup0. Add strnlen, which was a missing dependency already.