godoc/analysis: remove obsolete comment.
godoc/analysis: remove obsolete comment.

The bug it refers to is now fixed, and the alternative
implementation it suggests is not an improvement.

LGTM=gri
R=gri
CC=golang-codereviews
https://codereview.appspot.com/151620044

bryanxu/go-zh.tools,webfd/go-zh.tools,webfd/go-zh.tools,webfd/go-zh.tools,bryanxu/go-zh.tools,d0f/go-zh.tools,webfd/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools,bryanxu/go-zh.tools,webfd/go-zh.tools,d0f/go-zh.tools,d0f/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools