remove submodule
Squashed 'import/collada/' content from commit 0ef38b2

git-subtree-dir: import/collada
git-subtree-split: 0ef38b2d2034a8e6ee35d4e18f47c7a5e9014cd4
Merge commit 'a1c8a2c1083f90d454d6dbb868ebbc47fab93cbd' as 'import/collada'
get mat4's pointer method removed, and using value_ptr.