Fix removal of DNS record after completion

Changes undocumented API function to `dns/records/$_domain_name`.  
Since it checks for root right before asking for the ID, there is not need to check again and the `$_domain_name` should be accurate.  
Just changed the function name and it worked for me (no need to patch sed), but not sure why the other patch wants to change the sed call.  
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API Reference: https://www.dynu.com/en-US/Resources/API/Documentation#DNSRecords

dnsapi/dns_dynu.sh

@@ -152,7 +152,7 @@ _get_recordid() {
   fulldomain=$1
   txtvalue=$2
 
-  if ! _dynu_rest GET "dns/record/get?hostname=$fulldomain&rrtype=TXT"; then
+  if ! _dynu_rest GET "dns/records/$_domain_name"; then
     return 1
   fi