Flag incompatible_remove_native_git_repository

We're moving away from native git_repository rules to the Starlark versions of git_repository. Those can be loaded via load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository", "new_git_repository") and provide the same functionality.

By this change we no longer have to embedd jgit into bazel, thus making the bazel binary smaller and with less dependencies to maintain. Instead, we assume that users of git repositories have a git binary installed on their host system anyway. By calling git directly all global git configurations are honored as well.