Update OWNERS for base/allocator.

And base/allocator/partition_allocator.

Bug: None
Change-Id: I9c98833294ef489bce2fbb204f7b00e3fa9907e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2506429Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Matthew Denton <mpdenton@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Chris Palmer <palmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828992}

base/allocator/OWNERS

+lizeb@chromium.org
 primiano@chromium.org
 wfh@chromium.org

base/allocator/partition_allocator/OWNERS

@@ -3,4 +3,3 @@ bartekn@chromium.org
 haraken@chromium.org
 lizeb@chromium.org
 palmer@chromium.org
-tsepez@chromium.org