This reverts commit 5c4b8056.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Clusterfuzz%20Linux%20MSAN%20no%20origins/14661

Original change's description:
> [snapshot] Extract more files
> 
> This moves:
> 
> - ExternalReferenceEncoder to codegen/external-reference-encoder.h
> - SerializerDeserializer to snapshot/serializer-deserializer.h
> - Checksum() to snapshot/snapshot-utils.h
> 
> serializer-common.h and .cc are removed.
> 
> Tbr: clemensb@chromium.org,ulan@chromium.org
> Bug: v8:10416
> Change-Id: I36a242dcc1ad8833374aa567f73e0d4a75632c58
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144118
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Dan Elphick <delphick@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67281}

TBR=ulan@chromium.org,jgruber@chromium.org,clemensb@chromium.org,delphick@chromium.org

Change-Id: I718ca43a31d3ca937d700eab9bacc163e4598283
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10416
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157383Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67282}