Deleting an editor while currentEditorChanged is apparently not a good idea.
Use a queued connection instead.

This reverts commits 243a6259 and
d9602ca5.

Task-number: QTCREATORBUG-10190
Task-number: QTCREATORBUG-10235
Change-Id: Iccbee25fb77714963faa6f7184d1f5f53ed348a6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>