tour: delete the web pages

“A Tour of Go” moved to golang.org/x/website in CL 322790.
The supporting packages stay.

We may also use this repo for some other tours in the future.

Change-Id: Icb60bb9c1e4fe2e9b532108e3aefab24715c7c91
Reviewed-on: https://go-review.googlesource.com/c/tour/+/324309
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

gotour: link to Chinese translation of A Tour of Go

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/5410044