Fix warning related to missing-variable-declarations, remove unused global variables.

Signed-off-by: Jackie9527 <[email protected]>

code/AssetLib/SIB/SIBImporter.cpp

@@ -85,7 +85,7 @@ static const aiImporterDesc desc = {
 struct SIBChunk {
     uint32_t Tag;
     uint32_t Size;
-} PACK_STRUCT;
+};
 
 enum {
     POS,