Revert "go/printer: forbid empty line before first comment in block"

Revert "go/printer: forbid empty line before first comment in block"

This reverts commit 08f19bbde1b01227fdc2fa2d326e4029bb74dd96.

Reason for revert:
The changed transformation takes effect on a larger set
of code snippets than expected.

For example, this:
    func foo() {

        // Comment
        bar()

    }
becomes:
    func foo() {
        // Comment
        bar()

    }

This is an unintended consequence.

Change-Id: Ifca88d6267dab8a8170791f7205124712bf8ace8
Reviewed-on: https://go-review.googlesource.com/81335
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Joe Tsai <joetsai@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>