The `processed` variable local to `git_indexer_append` counts how many
objects have already been processed. But actually, whenever it gets
assigned to, we are also assigning the same value to the
`stats->indexed_objects` struct member. So in fact, it is being quite
useless due to always having the same value as the `indexer_objects`
member and makes it a bit harder to understand the code. We can just
remove the variable to fix that.