According to RFC-3986, the sub-delims chars should not be escaped in
fragment.
So this change fixes current behavior a bit.

Fixes #19917

Change-Id: I1a8deb93255d979532f75bae183c3fb53a05d395
Reviewed-on: https://go-review.googlesource.com/61650Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>