Drop the unused code for the old bridge removal warning

We used to have a custom modal dialog for the bridge removal, but at a certain point we removed.

However, we still have its CSS, which we could just remove.

added Doing label

assigned to @pierov

added Desktop label

mentioned in merge request !819 (merged)

removed Doing label

closed

marked this issue as related to tor-browser-build#40965 (closed)