drop script 'rotate-ntp'

For RouterOS 6.x a separate package 'ntp' exists. This adds server
functionality, but allows ip addresses for the client only. I added the
script 'rotate-ntp' to update addresses from names...

Now with RouterOS 7.x there's no extra package and the limitation does
no longer exist. So let's just drop the script.

This adds migration code, that...
 * removes the script from configuration
 * removes a scheduler from configuration
 * sets the configured ntp pool name for ntp client

doc/rotate-ntp.md

@@ -1,43 +1,3 @@
-Rotate NTP servers
-==================
-
-[◀ Go back to main README](../README.md)
-
-> ℹ️ **Info**: This script can not be used on its own but requires the base
-> installation. See [main README](../README.md) for details.
-
-Description
------------
-
-RouterOS requires NTP servers to be configured by IP address. Servers from a
-pool may appear and disappear, leaving broken NTP configuration.
-
-This script allows to rotate IP addresses from a given pool.
-
-Requirements and installation
------------------------------
-
-Just install the script:
-
-    $ScriptInstallUpdate rotate-ntp;
-
-Configuration
--------------
-
-The configuration goes to `global-config-overlay`, this is the parameter:
-
-* `NtpPool`: dns name of ntp server pool
-
-Usage and invocation
---------------------
-
-Just run the script to update the NTP configuration with actual IP
-addresses from pool if required.
-
-Alternatively a scheduler can be created:
-
-    /system/scheduler/add interval=5d name=rotate-ntp on-event="/system/script/run rotate-ntp;" start-time=startup;
-
----
-[◀ Go back to main README](../README.md)  
-[▲ Go back to top](#top)
+This script has been dropped as the limitation does no longer exist with
+RouterOS 7.x, where you can enable a ntp server and use a name for the client
+at the same time.