Remove length checking from TxtNoMultipleStrings (#1308)

All functions in should test for only one condition. There already is a
function that tests for long TXT records: TxtNoLongStrings.
Add calls to TxtNoLongStrings in all providers that use
TxtNoMultipleStrings, to keep functionality, except for NS1 and ClouDNS,
which allow for any TXT record length, but not for multiple strings per
TXT.

providers/msdns/auditrecords.go

@@ -14,6 +14,10 @@ func AuditRecords(records []*models.RecordConfig) error {
 	}
 	// Still needed as of 2021-03-01
 
+	if err := recordaudit.TxtNoLongStrings(records); err != nil {
+		return err
+	}
+
 	if err := recordaudit.TxtNotEmpty(records); err != nil {
 		return err
 	}