patching libgltf: stop a huge memory leak

It is ambiguos where we should free file buffers because they
are allocated by the caller code, but since gltfHandle is
deallocated inside libgltf and libgltf has a gltf_renderer_release
method for deallocation it seems better to free them by libgltf.

Change-Id: If3d9abed0514128c13cde8c1967ea80c4d27bf59