Revert "Issue #3070375 by lauriii, sacarney: Hidden buttons in off-canvas dialog are not being hidden"

This reverts commit 52fedda6.

Revert "Revert "Issue #3070375 by lauriii, jungle, larowlan, sacarney: [backport] Hidden buttons in off-canvas dialog are not being hidden""

This reverts commit 184a6126.

Revert "Issue #3070375 by lauriii, jungle, larowlan, sacarney: [backport] Hidden buttons in off-canvas dialog are not being hidden"

This reverts commit 3d7f169f.

Issue #2986147 by Wim Leers, mroycroft, rp7, sacarney, dkontorovsky: Autogrow for non-admin users causes CKEditor grow past the viewport when there is a lot of content in the CKEditor