Update libgit2 binaries to eb04744

https://github.com/libgit2/libgit2/compare/7940036...eb04744
Make OdbBackend interface ObjectId based
Enforce OdbBackend test coverage
Prove that #379 is fixed in libgit2
Add TreeDefinition.Remove(IEnumerable<string>)
Add RewriteHistoryOptions.PruneEmptyCommits