LICENSE.valgrind is a stale copy of src/third_party/valgrind/LICENSE

Change-Id: I274ad8cbe4e347979a9152b3a31c4598d2525aa4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2398458Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69873}