This reverts commit 712b66da.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20-%20builder/builds/32049

Original change's description:
> [build] Remove legacy isolate configurations
> 
> Bug: chromium:669910
> Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
> Change-Id: Iad58563fd4bb35501493f88af83362b1206a186c
> Reviewed-on: https://chromium-review.googlesource.com/982630
> Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52267}

TBR=machenbach@chromium.org,yangguo@chromium.org,sergiyb@chromium.org,jgruber@chromium.org

Change-Id: I1955325b0b419b38d793ab205131de8de08cb50a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:669910
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/983418Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52268}