ddns-scripts: remove postinst and prerm script call

ddns-scripts: remove postinst and prerm script call

For reasons that have not been investigated in detail, the package blocks
during 'postinst' with the new 'apk' backend when the package is installed
on the target.

After much back and forth, it turned out that the '/etc/init.d/ddns start'
command is responsible for this. The call is blocking.

The command '/etc/init.d/ddns enabled' in the 'postinst' also makes no sense
here, as it only checks whether the ddns service is enabled. The return value
is not checked at all. And the 'prerm' script is also not needed, as the
calls made there are implicitly called during package deinstallation.

Therefore, this commit removes the entire and not needed 'postinst' and
'prerm' script call.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>