Revert "TXT record attests ownership for the Public Suffix List"

This reverts commit dea655a990.

The Public Suffix List (PSL) denied our pull request to add sslip.io to
their list: <https://github.com/publicsuffix/list/pull/2206>

So there's no reason to keep their TXT record around; it only adds to
the clutter.

integration_test.go

@@ -176,10 +176,6 @@ var _ = Describe("sslip.io-dns-server", func() {
 				"@localhost sslip.io +short +vc",
 				`\A78.46.204.247\n\z`,
 				`TypeA sslip.io. \? 78.46.204.247\n`),
-			Entry(`TXT for _psl sslip.io is a link to the pull request for putting sslip.io on the Public Suffix List`,
-				"@localhost _psl.sslip.io txt +short",
-				`\A"https://github.com/publicsuffix/list/pull/2206"\n\z`,
-				`TypeTXT _psl.sslip.io. \? \["https://github.com/publicsuffix/list/pull/2206"\]`),
 		)
 	})
 	Describe("for more complex assertions", func() {

xip/xip.go

@@ -194,14 +194,6 @@ var (
 				}, nil
 			},
 		},
-		"_psl.sslip.io.": { // avoid Let's Encrypt rate limits by joining https://publicsuffix.org
-			TXT: func(x *Xip, _ net.IP) ([]dnsmessage.TXTResource, error) {
-				x.Metrics.AnsweredTXTVersionQueries++
-				return []dnsmessage.TXTResource{
-					{TXT: []string{"https://github.com/publicsuffix/list/pull/2206"}},
-				}, nil
-			},
-		},
 		"metrics.status.nip.io.": {
 			TXT: TXTMetrics,
 		},