This reverts commit 64c12860.

Reason for revert: the number of buckets can be changed later, so we can't cache the value

Original change's description:
> [OrderedHashSet] Remove extra entry lookup
> 
> Bug: v8:5717
> Change-Id: I999ea81f745a25a1f3a539e50594e597e64f5287
> Reviewed-on: https://chromium-review.googlesource.com/481044
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#44705}

TBR=adamk@chromium.org,cbruni@chromium.org,gsathya@chromium.org,v8-reviews@googlegroups.com
# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Iade35c0041e943f6dedb24844b07034f56ff1150
Reviewed-on: https://chromium-review.googlesource.com/483904
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44761}