dynamic dns: if we change/split these scripts, we can also rename them

".update" does not bring any value to the table, especially since there
is no other script there and the intent is somewhat clear...

plist

@@ -83,7 +83,7 @@
 /usr/local/etc/rc.d/configd
 /usr/local/etc/rc.d/flowd_aggregate
 /usr/local/etc/rc.d/netflow
-/usr/local/etc/rc.dyndns.update
+/usr/local/etc/rc.dyndns
 /usr/local/etc/rc.expireaccounts
 /usr/local/etc/rc.filter_configure
 /usr/local/etc/rc.filter_synchronize
@@ -129,7 +129,7 @@
 /usr/local/etc/rc.reload_interfaces
 /usr/local/etc/rc.resolv_conf_generate
 /usr/local/etc/rc.restart_webgui
-/usr/local/etc/rc.rfc2136.update
+/usr/local/etc/rc.rfc2136
 /usr/local/etc/rc.shutdown
 /usr/local/etc/rc.sshd
 /usr/local/etc/rc.syshook

src/etc/inc/plugins.inc.d/dyndns.inc

@@ -81,7 +81,7 @@ function dyndns_cron()
     $jobs = array();
 
     if (dyndns_enabled()) {
-        $jobs[]['autocron'] = array('/usr/local/etc/rc.dyndns.update', '11', '1');
+        $jobs[]['autocron'] = array('/usr/local/etc/rc.dyndns', '11', '1');
     }
 
     return $jobs;

src/etc/inc/plugins.inc.d/rfc2136.inc

@@ -78,7 +78,7 @@ function rfc2136_cron()
     $jobs = array();
 
     if (rfc2136_enabled()) {
-        $jobs[]['autocron'] = array('/usr/local/etc/rc.rfc2136.update', '16', '1');
+        $jobs[]['autocron'] = array('/usr/local/etc/rc.rfc2136', '16', '1');
     }
 
     return $jobs;

src/opnsense/service/conf/actions.d/actions_dyndns.conf

 [reload]
-command:/usr/local/etc/rc.dyndns.update
+command:/usr/local/etc/rc.dyndns
 description:Dynamic DNS Update
 parameters:%s
 type:script

src/opnsense/service/conf/actions.d/actions_rfc2136.conf

 [reload]
-command:/usr/local/etc/rc.rfc2136.update
+command:/usr/local/etc/rc.rfc2136
 description:RFC 2136 Update
 parameters:%s
 type:script