app.yaml: remove GOLANGORG_CHECK_COUNTRY
app.yaml: remove GOLANGORG_CHECK_COUNTRY

Nothing in this package or its dependencies uses this variable,
after CL 293449.

Change-Id: I82972cbb7abbeff6c3f4ca757c61ba966b666c19
Reviewed-on: https://go-review.googlesource.com/c/tour/+/295489
Trust: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/tour