lnd: evaluate timestamp at sv start time

a previous commit 8d6ec7b was missing an escaped $ sign which made the
"date" command evaluate at sysupdates execution, not sv start time.

lnd/env

@@ -41,7 +41,7 @@ lnd_svc_install() {
 exec 2>&1
 # wait for OS to acquire a clock sync.
 # random date in the past: Oct 22 06:40:00 PM UTC 2023
-while [ "$(date +%s)" -lt 1698000000 ]
+while [ "\$(date +%s)" -lt 1698000000 ]
 do
     echo "service start suspended until clock sync"
     sleep 5