This reverts commit 3b93e695.

Reason for revert: Breaks Linux nosnap:
https://ci.chromium.org/buildbot/client.v8/V8%20Linux%20-%20nosnap%20-%20debug/19064

Original change's description:
> Add InstanceType for EphemeronHashTable
> 
> This will allow the GC to differentiate between regular HashTables and EphemeronHashTables.
> 
> Bug: chromium:844008
> Change-Id: I2f9009ac25eb117de03786b110dd362b829c5e9e
> Reviewed-on: https://chromium-review.googlesource.com/1089066
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@google.com>
> Cr-Commit-Position: refs/heads/master@{#53577}

TBR=ulan@chromium.org,tebbi@chromium.org,dinfuehr@google.com

Change-Id: I8f92d76e35ae419af937add9a0e70a288c604781
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:844008
Reviewed-on: https://chromium-review.googlesource.com/1090973Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53589}