Replaced per-sample validation define with global define in base class

Toggling validation via command line arguments is the preferred way anyway
Define was also added as a CMake option

examples/multiview/multiview.cpp

@@ -11,8 +11,6 @@
 #include "vulkanexamplebase.h"
 #include "VulkanglTFModel.h"
 
-#define ENABLE_VALIDATION false
-
 class VulkanExample : public VulkanExampleBase
 {
 public:
@@ -58,7 +56,7 @@ public:
 	const float zNear = 0.1f;
 	const float zFar = 256.0f;
 
-	VulkanExample() : VulkanExampleBase(ENABLE_VALIDATION)
+	VulkanExample() : VulkanExampleBase()
 	{
 		title = "Multiview rendering";
 		camera.type = Camera::CameraType::firstperson;