Roll back MXID and room pillification

[weeman1337]

closes element-hq/element-web#24817

Reverts c7acade

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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This change is marked as an internal change (Task), so will not be included in the changelog.

[andybalaam]

Reverts the important parts of #10267

[weeman1337]

Reverts the important parts of #10267

Yes, I've just added a link to the commit to the description.

[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-10370-to-staging
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 05e3fb09d6e2a51b7cccbb02b371be71423bbfd7
# Push it to GitHub
git push --set-upstream origin backport-10370-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-10370-to-staging.