go/packages: remove unnecessary TODO
go/packages: remove unnecessary TODO

See adonovan's comment here:
https://go-review.googlesource.com/c/tools/+/146757/6/go/packages/golist.go#330

Change-Id: I7885fc1e7787c6b265be345f8622476b69d14325
Reviewed-on: https://go-review.googlesource.com/c/147447
Reviewed-by: Ian Cottrell <52376736e5e84615ec49f9c1843b8acc178b1d8d@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools