Enable HTTP/2 requests

The HTTP/2 Rapid Reset vulnerability was fixed in Go 1.21.3, and
we're already deploying newer than that.

main.go

@@ -184,7 +184,6 @@ func main() {
 		TLSConfig: &tls.Config{
 			MinVersion: tls.VersionTLS12, // TLS 1.2 is now the lowest acceptable level
 		},
-		TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler), 0),
 	}
 
 	// Add gzip middleware