Remove unused libc dependency from c2rust-transpiler

Author: nnethercote

Cargo.lock

@@ -23,7 +23,6 @@ fern = { version = "0.6", features = ["colored"] }
 handlebars = "4.2"
 indexmap = { version = "1.0.1", features = ["serde-1"] }
 itertools = "0.10"
-libc = "0.2"
 log = "0.4"
 log-reroute = "0.1"
 pathdiff = "0.2"