core: reword polkit request a bit (#10524)

"killing" is very UNIX terminology, and not really what this is about.
Let's be more correct and say "send a UNIX signal" for the operation.

Otherwise things are really weird if users call "journalctl --rotate"
from the command line, which internally asks systemd to send SIGUSR2 to
to journald: when german locale is selected this asks the user — roughly
transliterated — whether they want to "eliminate" journald, which is
definitely not the intended meaning.

src/core/dbus-unit.c

@@ -434,7 +434,7 @@ int bus_unit_method_kill(sd_bus_message *message, void *userdata, sd_bus_error *
                         u,
                         "kill",
                         CAP_KILL,
-                        N_("Authentication is required to kill '$(unit)'."),
+                        N_("Authentication is required to send a UNIX signal to the processes of '$(unit)'."),
                         true,
                         message,
                         error);