kOwnerOffset is redundant after 8a437788
since we check the READ_ONLY_HEAP bit instead of MemoryChunk::owner_ in
heap-write-barrier-inl.h

Bug: v8:9183
Change-Id: Ia0fbb530c088b8a87c551a99cc29d8cf7bd118f5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1664341Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Auto-Submit: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#62253}