ProjectExplorer: Drop KitAspect::defaultValue()

The functionality of this function overlapped with KitAspect::setup(),
leading to unclear responsibilities and resulting in bugs such as the
one fixed by 776d54e435.
Therefore, we drop the defaultValue() function, merging its
implementation with setup() where applicable.

Change-Id: Iefa9c3df8b76e97ddf9ad388516621f7ea6558d4
Reviewed-by: hjk <hjk@qt.io>

src/plugins/qmakeprojectmanager/qmakekitinformation.cpp

@@ -91,12 +91,6 @@ QmakeKitAspect::QmakeKitAspect()
     setPriority(24000);
 }
 
-QVariant QmakeKitAspect::defaultValue(const Kit *k) const
-{
-    Q_UNUSED(k);
-    return QString();
-}
-
 QList<Task> QmakeKitAspect::validate(const Kit *k) const
 {
     QList<Task> result;