drop python2 from jsonschema deps

When we upgraded jsonschema to be python3-only, we didn't update all
of its deps.  Drop python2 from all the packages that only it was
using to clean up more.

BUG=chromium:1007152
TEST=CQ passes

Change-Id: I40ce74850b78542e8cfce3df5ad427a961d1ae37
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2585694
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Ren-Pei Zeng <kamesan@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
2 files changed