Switch to upstream libc crate

Now that the macOS OFD fcntl constants have been merged upstream,
we can use the official libc crate instead of the fork.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: anacrolix

Cargo.toml

@@ -73,8 +73,7 @@ user = ["feature"]
 zerocopy = ["fs", "uio"]
 
 [dependencies.libc]
-git = "https://github.com/anacrolix/rust-libc"
-branch = "macos-ofd-fcntl"
+version = "0.2.172"
 features = ["extra_traits", "const-extern-fn"]
 
 [dev-dependencies]