Revert "Reuse arch/mode discovery in deopt fuzzer"

This reverts commit a24c7c9a.

Reason for revert: Breaks some users' workflow where
--arch and --mode are used to determine the build path.

Original change's description:
> Reuse arch/mode discovery in deopt fuzzer
> 
> Bug: v8:6917
> Change-Id: I1b7169c8702c8649812b17579d38d64de676ed60
> Reviewed-on: https://chromium-review.googlesource.com/723420
> Commit-Queue: Michał Majewski <majeski@google.com>
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48838}

TBR=machenbach@chromium.org,majeski@google.com

Change-Id: If1f6e67eee17f11ec7547943ce084d18242f6875
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6917
Reviewed-on: https://chromium-review.googlesource.com/735442Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48869}