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/texture/texture.cpp

@@ -11,8 +11,6 @@
 #include <ktxvulkan.h>
 
 #define VERTEX_BUFFER_BIND_ID 0
-#define ENABLE_VALIDATION false
-
 // Vertex layout for this example
 struct Vertex {
 	float pos[3];
@@ -62,7 +60,7 @@ public:
 	VkDescriptorSet descriptorSet;
 	VkDescriptorSetLayout descriptorSetLayout;
 
-	VulkanExample() : VulkanExampleBase(ENABLE_VALIDATION)
+	VulkanExample() : VulkanExampleBase()
 	{
 		title = "Texture loading";
 		camera.type = Camera::CameraType::lookat;