scripts: remove bogus command substitution in systemd-autofs-restart.sh

When we want to just execute command (without capturing output), we must
not do it via $(cmd). With such form, shell first gets output of 'cmd',
and then evaluates it. If this is empty string, it is successfully
executed. If not empty, all breaks down.
https://jira.sw.ru/browse/PSBM-44207



Signed-off-by: Eugene Kolomeetz <klm@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>