Removed support for TXT resource record.

Like the HINFO and MINFO RR's, TXT is vulnerable to RCE attacks and has
no purpose at the moment. TXT may be needed in the future (e.g. data
exfiltration) which is why it has been removed separately.

extensions/dns/model.rb

@@ -167,14 +167,6 @@ module BeEF
               else
                 raise InvalidDnsResponseError, 'SOA'
               end
-            elsif resource == Resolv::DNS::Resource::IN::TXT
-              if resource.is_a?(String)
-                sprintf "t.respond!('%s')", response
-              elsif (response.is_a?(Symbol) && response.to_s =~ sym_regex) || response =~ sym_regex
-                sprintf "t.fail!(:%s)", response.to_sym
-              else
-                raise InvalidDnsResponseError, 'TXT'
-              end
             elsif resource == Resolv::DNS::Resource::IN::WKS
               if response.is_a?(Array)
                 unless BeEF::Filters.is_valid_ip?(resource[0]) &&