[lsan] Remove suppression for JSArrayBuffer::SetupAllocatingData.

I can't reproduce any issues with an lsan build, so we will remove
this for now and keep an eye out.

Bug: v8:6315
Change-Id: Iad2a1b23f3614ec9a09a83bb01e235969c3f9fcc
Reviewed-on: https://chromium-review.googlesource.com/542835Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46096}

tools/memory/lsan/suppressions.txt

@@ -13,4 +13,3 @@ leak:v8::internal::compiler::JumpThreading::ApplyForwarding
 
 # mjsunit
 leak:v8::internal::FuncNameInferrer::FuncNameInferrer
-leak:v8::internal::JSArrayBuffer::SetupAllocatingData