When a ChangesetList sleeps after a Quicksand navigation, also hide any visible banner

Summary: Fixes T13080. The banner wasn't properly included in the sleep/wake logic.

Test Plan:
Mentioned Dxxx on a task. Enabled persistent chat to activate Quicksand. Reloaded page. Clicked Dxxx. Scrolled down until a changeset header appeared. Pressed back button.

• Before patch: ended up on task, with header still around.
• After patch: ended up on task, with header properly vanquished.

Pressed "forward", ended up back on the revision with the header again.

Maniphest Tasks: T13080

Differential Revision: https://secure.phabricator.com/D19086