Revert "EditorManager: Fix crash when closing an editor upon activation"

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

This reverts commits 243a625961,
447c4ed37f,
d9602ca550 and
3103487038.

Change-Id: Iccbee25fb77714963faa6f7184d1f5f53ed348a6
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/cpptools/cppcompletion_test.cpp

@@ -31,7 +31,6 @@
 #include "cppcompletionassist.h"
 #include "cppmodelmanager.h"
 
-#include <coreplugin/plugintestutils.h>
 #include <texteditor/plaintexteditor.h>
 #include <texteditor/codeassist/iassistproposal.h>
 #include <texteditor/convenience.h>
@@ -92,7 +91,7 @@ public:
 
     ~CompletionTestCase()
     {
-        Core::Tests::closeAndDeleteEditor(editor);
+        EditorManager::closeEditor(editor, /*askAboutModifiedEditors=*/ false);
         cmm->GC();
         QVERIFY(cmm->snapshot().isEmpty());
     }