ProjectExplorer: Replace virtual BuildStepConfigWidget::showWidget

... by a bool member.

One reason less for the need of custom derived classes, i.e. one
step forward to a setup where the then-generic config widget can be
created in BuildStepListWidget::init() and filled with aspect-
created subwidget, reducing the need of per-BuildStep boilerplate
similar to what was done in RunConfiguration recently.

Task-number: QTCREATORBUG-19985
Change-Id: I85d26bdb6b35d0d6715782214328a40eef87286e
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/remotelinux/tarpackagecreationstep.cpp

@@ -56,6 +56,8 @@ class CreateTarStepWidget : public SimpleBuildStepConfigWidget
 public:
     CreateTarStepWidget(TarPackageCreationStep *step) : SimpleBuildStepConfigWidget(step)
     {
+        setShowWidget(true);
+
         m_ignoreMissingFilesCheckBox.setText(tr("Ignore missing files"));
         m_incrementalDeploymentCheckBox.setText(tr("Package modified files only"));
 
@@ -88,8 +90,6 @@ public:
             + step->packageFilePath();
     }
 
-    bool showWidget() const { return true; }
-
 private:
     void handleIgnoreMissingFilesChanged(bool ignoreMissingFiles) {
         TarPackageCreationStep *step = qobject_cast<TarPackageCreationStep *>(this->step());