vulkan: do not reinvent a queue context struct

We recently introduced a public field which was a superset
of the queue context we used to have.

Switch to using it entirely.

This also allows us to get rid of the NIH function which was
valid only for video queues.

libavcodec/vulkan_decode.h

@@ -46,7 +46,7 @@ typedef struct FFVulkanDecodeProfileData {
 typedef struct FFVulkanDecodeShared {
     FFVulkanContext s;
     FFVkVideoCommon common;
-    FFVkQueueFamilyCtx qf;
+    AVVulkanDeviceQueueFamily *qf;
     FFVkExecPool exec_pool;
 
     AVBufferPool *buf_pool;