Importing libbpf-sys, but have removed .gitmodules and the libbpf,
elfutils, and zlib submodules. We will use the libraries in the android
tree to satisfy these dependencies.

Request Document: go/android-rust-importing-crates
For CL Reviewers: go/android3p#cl-review
For Build Team: go/ab-third-party-imports
Bug: 360132854
Bug: 359646531
Test: none
Change-Id: I42f3c771075c9cf1f6045b6b33cae7cfc41a7024
Signed-off-by: Neill Kapron <nkapron@google.com>