[tools] Migrate to argparse module and remove few deprecated arguments

The --run-count-multiplier flag was used to run an experiment and is not needed
anymore. It will be superceeded by another parameter that will run benchmarks as
many times as needed until needed confidence is achieved.

R=machenbach@chromium.org

No-Try: true
No-Tree-Checks: true
Bug: chromium:880724
Change-Id: Iedd3d0f900a838f97cfa3339f582f6d02cce3e93
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578504
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60980}