QbsPM: Re-introduce uniqueProductName()

This patch prepares for enhancing information stored inside
buildSystemTarget.

Change-Id: I5d81fd01ab6b06c162f47fd9536de697ddfd24a3
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/qbsprojectmanager/qbsrunconfiguration.cpp

@@ -277,6 +277,11 @@ void QbsRunConfiguration::addToBaseEnvironment(Utils::Environment &env) const
 }
 
 QString QbsRunConfiguration::buildSystemTarget() const
+{
+    return productDisplayNameFromId(id());
+}
+
+QString QbsRunConfiguration::uniqueProductName() const
 {
     return m_uniqueProductName;
 }