Remove use of VK_LAYER_KHRONOS_validation

I have no idea what this is supposed to do, but it is causing the
demo app to crash with a LAYER_NOT_INITIALIZED error.

Volcano/Sources/Volcano/Instance.swift

@@ -51,8 +51,7 @@ public final class Instance: SharedPointerStorage<VkInstance_T> {
     public init(extensions: Set<InstanceExtension> = []) {
         do {
             let vulkanVersion: CUnsignedInt = (1 << 22) | (3 << 12) | 0
-
-            var layers: [String] = []
+            let layers: [String] = []
 
             var extensions = extensions + [
                 .getPhysicalDeviceProperties2Khr,
@@ -65,11 +64,6 @@ public final class Instance: SharedPointerStorage<VkInstance_T> {
                 extensions.insert(.externalFenceCapabilitiesKhr)
             #endif
 
-            #if DEBUG
-                layers.append("VK_LAYER_KHRONOS_validation")
-                extensions.insert(.debugUtilsExt)
-            #endif
-
             let handle = try VkInstanceCreateInfo.lava {
                 (\.enabledLayerCount, \.ppEnabledLayerNames) <- layers
                 \.pApplicationInfo <- {