vulkan: Delete staged encoders and staging streams.

This fixes a memory leak when destorying the staging info.

TEST=fuchsia scenic_tests.

Change-Id: Ic1ca57fa0bd685638c9fb05a971714e0eb0f9d71
diff --git a/system/vulkan_enc/ResourceTracker.cpp b/system/vulkan_enc/ResourceTracker.cpp
index cb74edd..a37d778 100644
--- a/system/vulkan_enc/ResourceTracker.cpp
+++ b/system/vulkan_enc/ResourceTracker.cpp
@@ -239,6 +239,16 @@
     std::vector<CommandBufferStagingStream*> streams;
     std::vector<VkEncoder*> encoders;
 
+    ~StagingInfo() {
+        for (auto stream : streams) {
+            delete stream;
+        }
+
+        for (auto encoder : encoders) {
+            delete encoder;
+        }
+    }
+
     void pushStaging(CommandBufferStagingStream* stream, VkEncoder* encoder) {
         AutoLock lock(mLock);
         stream->reset();