BuildStep: Drop using ProjectConfiguration::parent

The parent function isn't used anymore after the amended change.
Originally, it was introduced in
9d206a2bc4, when things still relied
on QObject hierarchy.

Amends 06a57f8c42

Change-Id: I9e3a2bbaf4c4cac308a18cbe5cf5905f2655443f
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/buildstep.h

@@ -130,8 +130,6 @@ protected:
     void setCancelMessage(const QString &message);
 
 private:
-    using ProjectConfiguration::parent;
-
     friend class BuildManager;
     virtual Tasking::GroupItem runRecipe() = 0;