UI: Remove ifdefs for Qt 5.9 and older

Among the systems we officially support, the oldest Qt version is Qt 5.9
on Ubuntu 18.04. We should be able to safely remove these ifdefs.

UI/window-basic-main.cpp

@@ -4741,7 +4741,7 @@ void OBSBasic::AddProjectorMenuMonitors(QMenu *parent, QObject *target,
 		fullname << ")";
 #elif defined(__APPLE__)
 		name = screen->name();
-#elif QT_VERSION >= QT_VERSION_CHECK(5, 9, 0)
+#else
 		name = screen->model().simplified();
 
 		if (name.length() > 1 && name.endsWith("-"))
@@ -8006,7 +8006,6 @@ void OBSBasic::on_resetUI_triggered()
 
 	restoreState(startingDockLayout);
 
-#if QT_VERSION >= QT_VERSION_CHECK(5, 6, 0)
 	int cx = width();
 	int cy = height();
 
@@ -8033,7 +8032,6 @@ void OBSBasic::on_resetUI_triggered()
 
 	resizeDocks(docks, {cy, cy, cy, cy, cy}, Qt::Vertical);
 	resizeDocks(docks, sizes, Qt::Horizontal);
-#endif
 
 	activateWindow();
 }