core/service: fix deserialization of non-absolute commands

We'd fail with:
Apr 23 10:58:26 systemd[1]: Deserializing state...
Apr 23 10:58:26 systemd[1]: testsuite-01.service: Failed to parse serialized command "ExecStart 0 sh "sh" "-e" "-x" "-c" "systemctl --state=failed --no-legend --no-pager >/failed ; systemctl daemon-reload ; echo OK >/testok"": Invalid argument
Apr 23 10:58:26 systemd[1]: testsuite-01.service: Reinstalled deserialized job testsuite-01.service/start as 209

This was missed in 5008da1ec1, and apparently nobody noticed until now :(

src/core/service.c

@@ -2783,9 +2783,6 @@ static int service_deserialize_exec_command(
                 case STATE_EXEC_COMMAND_PATH:
                         path = TAKE_PTR(arg);
                         state = STATE_EXEC_COMMAND_ARGS;
-
-                        if (!path_is_absolute(path))
-                                return -EINVAL;
                         break;
                 case STATE_EXEC_COMMAND_ARGS:
                         r = strv_extend(&argv, arg);