cmd/cgo: remove unnecessary nil check

commentText is only called if g != nil in ParseGo, so the check inside
commentText is redundant and can be deleted.

Change-Id: I130c18b738527c96bc59950b354a50b9e23f92e9
Reviewed-on: https://go-review.googlesource.com/74871
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/cgo/ast.go

@@ -144,9 +144,6 @@ func (f *File) ParseGo(name string, src []byte) {
 // Like ast.CommentGroup's Text method but preserves
 // leading blank lines, so that line numbers line up.
 func commentText(g *ast.CommentGroup) string {
-	if g == nil {
-		return ""
-	}
 	var pieces []string
 	for _, com := range g.List {
 		c := com.Text