Disable Vulkan debug layers by default

The vast majority of Vulkan code running in Moonlight
is part of FFmpeg or libplacebo, so the debug layers
really just slow things down without finding any bugs
in our code.

Additionally, there are some overzealous checks firing
constantly on libplacebo and FFmpeg with certain Vulkan
drivers that we can't do anything about.

Author: cgutman

app/streaming/video/ffmpeg-renderers/plvk.cpp

@@ -378,14 +378,8 @@ bool PlVkRenderer::initialize(PDECODER_PARAMETERS params)
 
     pl_vk_inst_params vkInstParams = pl_vk_inst_default_params;
     {
-        bool ok;
-        vkInstParams.debug_extra = !!qEnvironmentVariableIntValue("PLVK_DEBUG_EXTRA", &ok);
-        vkInstParams.debug = vkInstParams.debug_extra || !!qEnvironmentVariableIntValue("PLVK_DEBUG", &ok);
-#ifdef QT_DEBUG
-        if (!ok) {
-            vkInstParams.debug = true;
-        }
-#endif
+        vkInstParams.debug_extra = !!qEnvironmentVariableIntValue("PLVK_DEBUG_EXTRA");
+        vkInstParams.debug = vkInstParams.debug_extra || !!qEnvironmentVariableIntValue("PLVK_DEBUG");
     }
     vkInstParams.get_proc_addr = (PFN_vkGetInstanceProcAddr)SDL_Vulkan_GetVkGetInstanceProcAddr();
     vkInstParams.extensions = instanceExtensions.data();