Revert "cmd/gofmt: fix symlink file truncation"

This reverts commit 5f711bfdb35cc26413b86785f58b7ed37a25a0dc.

Reason for revert: Doubts about correctness of fix. Will revisit.

Change-Id: I8fca8705fbba6ab02332c1b99fa9a7e775a16326
Reviewed-on: https://go-review.googlesource.com/c/go/+/785060
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>