bytes: correct comment about usage of bytes.Buffer by Printf

The fmt package does not use bytes.Buffer
anymore as an internal buffer.

Change-Id: I34c7a52506290ccbcb10ea2e85dea49a0a8b8203
Reviewed-on: https://go-review.googlesource.com/20511
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/bytes/buffer.go

@@ -18,7 +18,7 @@ type Buffer struct {
 	buf       []byte            // contents are the bytes buf[off : len(buf)]
 	off       int               // read at &buf[off], write at &buf[len(buf)]
 	runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each call to WriteRune
-	bootstrap [64]byte          // memory to hold first slice; helps small buffers (Printf) avoid allocation.
+	bootstrap [64]byte          // memory to hold first slice; helps small buffers avoid allocation.
 	lastRead  readOp            // last read operation, so that Unread* can work correctly.
 }