Remove suggestion we will store Git repos in DBs
'Custom backends' for libgit2 seem to be an abandoned idea, see:
https://github.com/libgit2/libgit2-backends/pull/4#issuecomment-36115322
Where one of the libgit2 developers writes:
There is no way that this is not going to be noticeably slower than using the disc and letting the kernel put the data directly in libgit2's memory space.