Revert "bot_update: make --output_json required in script invocation."

This reverts commit 331a276b.

Reason for revert: Breaks everything:
https://build.chromium.org/p/chromium/buildstatus?builder=Win&number=60914

Original change's description:
> bot_update: make --output_json required in script invocation.
> 
> It's already set by recipe, so this should have 0 difference in prod.
> 
> R=​iannucci@chromium.org
> 
> Bug:
> Change-Id: I1e1129b9748d6647e45eb26892c8e892019fe088
> Reviewed-on: https://chromium-review.googlesource.com/769164
> Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
> Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

TBR=iannucci@chromium.org,tandrii@chromium.org

Change-Id: Ifc40a5f89c9c770f6c0fc02aed024a6ba5f693cb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/777659Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>