This reverts commit 087e95ba.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [Compiler] Use IdentityMap to store jobs in CompilerDispatcher.
> 
> Stores jobs in an IdentityMap keyed by their SharedFunctionInfo to enable
> fast checking of whether a job is enqueued.
> 
> BUG=v8:5203
> 
> Change-Id: I6c37972093515a27077f79594cad27e32e1a4e7c
> Reviewed-on: https://chromium-review.googlesource.com/444768
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#43370}

TBR=rmcilroy@chromium.org,jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5203

Change-Id: I5d1101bdae6939378dad595b26698fe2aaaad35e
Reviewed-on: https://chromium-review.googlesource.com/446357Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43372}