test: re-enable tests that had a false requirement on coreutils' kill

Recently we've not built our kill command by default,
so reduce test dependence on that.

* tests/sort/sort-compress-proc.sh: `kill -l [exit_status]` is well
supported, and is a POSIX requirement.
* tests/timeout/timeout.sh: There were actually no kill invocations
in this test at all.

tests/timeout/timeout.sh

@@ -17,7 +17,7 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
-print_ver_ timeout kill
+print_ver_ timeout
 require_trap_signame_
 
 # no timeout