Add fissionEnabled to new uninstall ping

[jklukas]

I think this is a weird ordering problem where the tests succeeded on
#629
but after merging, it was out of date with the new fissionEnabled field.

Checklist for reviewer:

• Commits should reference a bug or github issue, if relevant (if a bug is referenced, the pull request should include the bug number in the title)
• Scan the PR and verify that no changes (particularly to .circleci/config.yml) will cause environment variables (particularly credentials) to be exposed in test logs
• If the PR comes from a fork, trigger the integration CI test by pushing this revision as discussed in the README and review the report posted in the comments.

For glean changes:

• Update templates/include/glean/CHANGELOG.md

[dataops-ci-bot]

Integration report for "Add fissionEnabled to new uninstall ping"

bq_schema_0f34b318-bbda4355.diff

Click to expand!

diff /app/integration/0f34b318/telemetry.uninstall.4.bq /app/integration/bbda4355/telemetry.uninstall.4.bq
717a718,723
>             "description": "whether fission is enabled this session, and subframes can load in a different process",
>             "mode": "NULLABLE",
>             "name": "fission_enabled",
>             "type": "BOOL"
>           },
>           {