Remove outdated tests/README

We'll write a new section about this later on

Change-Id: I0c7d00efdd1b37c9ef854a17f2a4c9bbd66e4d37
Reviewed-on: http://review.couchbase.org/41445
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>