remove libgit2 submodule
move libgit2 under deps/
Squashed 'deps/libgit2/' content from commit 2b40390

git-subtree-dir: deps/libgit2
git-subtree-split: 2b40390f226ac8ba516fdf0d893e0b5a29857dc7
Merge commit '2622686e95c481f9d6628e50dbc699de6d81faf2' as 'deps/libgit2'
t: use libgit2/TestGitRepository.git repo in remote tests