Revert "fix(nslord): create keys when quickly recreating a deleted zone"

This reverts commit d6fb735f5710f6be8e15722ae9308ac1b6e4e1fe.

The commit was a workaround which is unnecessary with pdns 4.2, see #106.

nslord/conf/pdns.conf.var

@@ -26,4 +26,3 @@ gmysql-dnssec=yes
 cache-ttl=${DESECSTACK_NSLORD_CACHE_TTL}
 negquery-cache-ttl=${DESECSTACK_NSLORD_CACHE_TTL}
 query-cache-ttl=${DESECSTACK_NSLORD_CACHE_TTL}
-dnssec-key-cache-ttl=0