internal/format: drop go-fuzz test case

We were not running it in CI, so it had rotted or was going to rot.
We'll replace it with a native fuzz test once that's ready.

internal/format/Dockerfile.go-fuzz

@@ -1,21 +0,0 @@
-# Copyright 2019 Google LLC
-#
-# Use of this source code is governed by a BSD-style
-# license that can be found in the LICENSE file or at
-# https://developers.google.com/open-source/licenses/bsd
-
-# docker run --rm -v $PWD/workdir:/workdir $(docker build -q -f internal/format/Dockerfile.go-fuzz .)
-
-FROM golang:1.14-alpine3.11
-
-RUN apk add --no-cache git
-RUN go get github.com/dvyukov/go-fuzz/...
-
-ADD . $GOPATH/src/filippo.io/age/
-WORKDIR $GOPATH/src/filippo.io/age
-
-RUN go-fuzz-build ./internal/format
-
-VOLUME /workdir
-
-ENTRYPOINT ["go-fuzz", "-workdir", "/workdir", "-bin", "format-fuzz.zip"]

internal/format/format_gofuzz.go

@@ -1,60 +0,0 @@
-// Copyright 2019 Google LLC
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-
-// +build gofuzz
-
-package format
-
-import (
-	"bytes"
-	"fmt"
-	"io"
-	"strings"
-
-	"github.com/sergi/go-diff/diffmatchpatch"
-)
-
-func Fuzz(data []byte) int {
-	isArmored := bytes.HasPrefix(data, []byte("-----BEGIN AGE ENCRYPTED FILE-----"))
-	h, payload, err := Parse(bytes.NewReader(data))
-	if err != nil {
-		if h != nil {
-			panic("h != nil on error")
-		}
-		if payload != nil {
-			panic("payload != nil on error")
-		}
-		return 0
-	}
-	w := &bytes.Buffer{}
-	if isArmored {
-		w := ArmoredWriter(w)
-		if err := h.Marshal(w); err != nil {
-			panic(err)
-		}
-		if _, err := io.Copy(w, payload); err != nil {
-			if strings.Contains(err.Error(), "invalid armor") {
-				return 0
-			}
-			panic(err)
-		}
-		w.Close()
-	} else {
-		if err := h.Marshal(w); err != nil {
-			panic(err)
-		}
-		if _, err := io.Copy(w, payload); err != nil {
-			panic(err)
-		}
-	}
-	if !bytes.Equal(w.Bytes(), data) {
-		dmp := diffmatchpatch.New()
-		diffs := dmp.DiffMain(string(data), string(w.Bytes()), false)
-		fmt.Println(dmp.DiffToDelta(diffs))
-		panic("Marshal output different from input")
-	}
-	return 1
-}