[GUI] Remove explicit triangle styling from tabs

On Windows the lower tabs of the PropertyView were being set to
triangular, which breaks stylesheets. This removes that code, so they
now take on whatever the standard shape is on the system.

Fixes #4599

src/Gui/PropertyView.cpp

@@ -89,9 +89,6 @@ PropertyView::PropertyView(QWidget *parent)
     tabs = new QTabWidget (this);
     tabs->setObjectName(QString::fromUtf8("propertyTab"));
     tabs->setTabPosition(QTabWidget::South);
-#if defined(Q_OS_WIN32)
-    tabs->setTabShape(QTabWidget::Triangular);
-#endif
     pLayout->addWidget(tabs, 0, 0);
 
     propertyEditorView = new Gui::PropertyEditor::PropertyEditor();