Remove sync.Pool from internal/repository

The pool was used improperly, causing more allocations to be
performed than without it.

name              old time/op    new time/op    delta
SaveAndEncrypt-8    36.8ms ± 2%    36.9ms ± 2%    ~     (p=0.218 n=10+10)

name              old speed      new speed      delta
SaveAndEncrypt-8   114MB/s ± 2%   114MB/s ± 2%    ~     (p=0.218 n=10+10)

name              old alloc/op   new alloc/op   delta
SaveAndEncrypt-8    21.1MB ± 0%    21.0MB ± 0%  -0.44%  (p=0.000 n=10+10)

name              old allocs/op  new allocs/op  delta
SaveAndEncrypt-8      79.0 ± 0%      77.0 ± 0%  -2.53%  (p=0.000 n=10+10)

internal/repository/pool.go

@@ -1,21 +0,0 @@
-package repository
-
-import (
-	"sync"
-
-	"github.com/restic/chunker"
-)
-
-var bufPool = sync.Pool{
-	New: func() interface{} {
-		return make([]byte, chunker.MaxSize/3)
-	},
-}
-
-func getBuf() []byte {
-	return bufPool.Get().([]byte)
-}
-
-func freeBuf(data []byte) {
-	bufPool.Put(data)
-}

internal/repository/repository.go

@@ -225,13 +225,10 @@ func (r *Repository) SaveAndEncrypt(ctx context.Context, t restic.BlobType, data
 
 	debug.Log("save id %v (%v, %d bytes)", id, t, len(data))
 
-	// get buf from the pool
-	ciphertext := getBuf()
-
-	ciphertext = ciphertext[:0]
 	nonce := crypto.NewRandomNonce()
+
+	ciphertext := make([]byte, 0, restic.CiphertextLength(len(data)))
 	ciphertext = append(ciphertext, nonce...)
-	defer freeBuf(ciphertext)
 
 	// encrypt blob
 	ciphertext = r.key.Seal(ciphertext, nonce, data, nil)

internal/repository/repository_test.go

@@ -104,6 +104,7 @@ func BenchmarkSaveAndEncrypt(t *testing.B) {
 
 	id := restic.ID(sha256.Sum256(data))
 
+	t.ReportAllocs()
 	t.ResetTimer()
 	t.SetBytes(int64(size))