cmd/coordinator: don't check for 'go tool dist'
cmd/coordinator: don't check for 'go tool dist'

It's been there for the past two releases. We can assume it's present.

Change-Id: I94ac107d4c52ea823d42a63ced571ff4c81532a2
Reviewed-on: https://go-review.googlesource.com/29471
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build