Remove unused libc from Cargo.toml

Our dependencies still drag it in, but it makes me feel better.

Author: jyn514

Cargo.toml

@@ -21,7 +21,6 @@ env_logger = "0.7"
 r2d2 = "0.8"
 r2d2_postgres = "0.14"
 url = "1.4"
-libc = "0.2"
 badge = { version = "0", path = "src/web/badge" }
 failure = "0.1.3"
 comrak = { version = "0.7", default-features = false }