ProjectExplorer: Fix a warning about disconnecting from destoyed() signal

Fix:
"QObject::disconnect: wildcard call disconnects from destroyed signal
of ProjectExplorer::TargetSetupPage::TargetSetupPage" warning.

It seems that the call to disconnect() isn't really needed these days.

Might be reproduced by executing:
bin/qtcreator -test CppEditor,testExtraeditorsupportUiFiles
or, like mentioned in the bug report, by loading a project
without .user file and by closing Creator.

Amends 33c732c60c

Task-number: QTCREATORBUG-16744
Change-Id: I54e77e249de7d0c65c62ff6b7b9972361d8bce69
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/targetsetuppage.cpp

@@ -164,7 +164,6 @@ QList<Id> TargetSetupPage::selectedKits() const
 
 TargetSetupPage::~TargetSetupPage()
 {
-    disconnect();
     d->reset();
     delete d->spacer;
     delete d;