Location of dEQP / VK-GL-CTS has moved, update doc/dEQP.md.

Bug: angleproject:3914
Change-Id: I705922b7292ffb60954042edae2514d515e68b44
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1887678Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>