This reverts commit 520b025f.

Reason for revert: Breaks internal-snapshot build: https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20-%20internal%20snapshot/builds/14603

Original change's description:
> Remove SFI code field
> 
> Remove the SharedFunctionInfo code field, inferring the code object
> from the function_data field instead. In some cases, the function_data
> field can now hold a Code object (e.g. some WASM cases).
> 
> Bug: chromium:783853
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
> Change-Id: I1219a4d6aa5abaa9fee54dda883da7a3186e347a
> Reviewed-on: https://chromium-review.googlesource.com/952452
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52064}

TBR=yangguo@chromium.org,mstarzinger@chromium.org,jgruber@chromium.org,leszeks@chromium.org,bmeurer@chromium.org,verwaest@chromium.org

Change-Id: Iaf464ed29ba4317bbbb255c1aec76fb65cddba84
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:783853
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/970647Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52066}