Revert "Set up key backup using non-deprecated APIs (#12005)"

[BillCarsonFr]

This reverts commit df11b90, and also adds a regression test.

Fixes element-hq/element-web#26814

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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Here's what your changelog entry will look like:

🐛 Bug Fixes

• Revert "Set up key backup using non-deprecated APIs (Set up key backup using non-deprecated APIs #12005)" (#12102). Fixes A fresh login creates a new key backup element-hq/element-web#26814.

[richvdh]

As I understand it, this will re-open element-hq/element-web#26323.

[richvdh]

lgtm

[richvdh]

lgtm.

@t3chguy are you happy to bypass the coverage gate on this?

[t3chguy]

Why is this going away?

[t3chguy]

Oh we also have getClipboardText - fun

[RiotRobot]

The backport to staging failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-staging staging
# Navigate to the new working tree
cd .worktrees/backport-staging
# Create a new branch
git switch --create backport-12102-to-staging
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 61070698cc6a758d9bcbbd783d5c0500af157fa7
# Push it to GitHub
git push --set-upstream origin backport-12102-to-staging
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-staging

Then, create a pull request where the base branch is staging and the compare/head branch is backport-12102-to-staging.