Temporarily disable autodiscardable tabs

[bbondy]

Fix #12916

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• [ x Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed. (Ask a Brave employee to help if you cannot access this document.)

Test Plan:

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[bridiver]

++

[bridiver]

cc @petemill

[petemill]

Great to reduce the impact of the issue for now

[bbondy]

master: d00d99c
0.21.x: 6bd26ca
0.20.x: fe4cee7