Remove submodules
Squashed 'lwip/' content from commit e7f3224

git-subtree-dir: lwip
git-subtree-split: e7f32240917cc912eb6e3e36780ecb3c4a06f264
Merge commit 'efdf7362455df181a485915ab3d7fa03db674bb7' as 'lwip'
Squashed 'lwip-contrib/' content from commit 36eab89

git-subtree-dir: lwip-contrib
git-subtree-split: 36eab8918473ab575ed11c87cee33954a52e6a1d
Merge commit 'e0a79defd2552a6517c95ffb7476a9e43a3c30b4' as 'lwip-contrib'