Make qmakestep and makestep deletable.

src/plugins/qt4projectmanager/makestep.cpp

@@ -149,7 +149,7 @@ QString MakeStep::displayName()
 
 bool MakeStep::immutable() const
 {
-    return true;
+    return false;
 }
 
 ProjectExplorer::BuildStepConfigWidget *MakeStep::createConfigWidget()

src/plugins/qt4projectmanager/qmakestep.cpp

@@ -175,7 +175,7 @@ ProjectExplorer::BuildStepConfigWidget *QMakeStep::createConfigWidget()
 
 bool QMakeStep::immutable() const
 {
-    return true;
+    return false;
 }