ProjectExplorer: Introduce a ProjectConfiguration::kit() function

For convenience, and use it in some places.

Change-Id: I8f7cb502b37b2fbf4cf2d17cac9c6299558332dc
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/remotelinux/tarpackagecreationstep.cpp

@@ -346,7 +346,7 @@ bool TarPackageCreationStep::runImpl()
     if (m_incrementalDeploymentAspect->value()) {
         m_files.clear();
         for (const DeployableFile &file : files)
-            addNeededDeploymentFiles(file, target()->kit());
+            addNeededDeploymentFiles(file, kit());
     } else {
         m_files = files;
     }