currency: disable flaky TestLinking
currency: disable flaky TestLinking

It fails on a bunch of builders and it's not clear what it's testing.

It hasn't been fixed since Oct 2016 so it gets disabled.

Updates golang/go#17538

Change-Id: I0f454c46b31b8306cc604c36ec6d06cc6ad703b5
Reviewed-on: https://go-review.googlesource.com/c/text/+/170783
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

golang/text